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diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt deleted file mode 100644 index 2d8d2fed7317..000000000000 --- a/Documentation/DMA-API.txt +++ /dev/null @@ -1,745 +0,0 @@ -============================================ -Dynamic DMA mapping using the generic device -============================================ - -:Author: James E.J. Bottomley <James.Bottomley@HansenPartnership.com> - -This document describes the DMA API. For a more gentle introduction -of the API (and actual examples), see Documentation/DMA-API-HOWTO.txt. - -This API is split into two pieces. Part I describes the basic API. -Part II describes extensions for supporting non-consistent memory -machines. Unless you know that your driver absolutely has to support -non-consistent platforms (this is usually only legacy platforms) you -should only use the API described in part I. - -Part I - dma_API ----------------- - -To get the dma_API, you must #include <linux/dma-mapping.h>. This -provides dma_addr_t and the interfaces described below. - -A dma_addr_t can hold any valid DMA address for the platform. It can be -given to a device to use as a DMA source or target. A CPU cannot reference -a dma_addr_t directly because there may be translation between its physical -address space and the DMA address space. - -Part Ia - Using large DMA-coherent buffers ------------------------------------------- - -:: - - void * - dma_alloc_coherent(struct device *dev, size_t size, - dma_addr_t *dma_handle, gfp_t flag) - -Consistent memory is memory for which a write by either the device or -the processor can immediately be read by the processor or device -without having to worry about caching effects. (You may however need -to make sure to flush the processor's write buffers before telling -devices to read that memory.) - -This routine allocates a region of <size> bytes of consistent memory. - -It returns a pointer to the allocated region (in the processor's virtual -address space) or NULL if the allocation failed. - -It also returns a <dma_handle> which may be cast to an unsigned integer the -same width as the bus and given to the device as the DMA address base of -the region. - -Note: consistent memory can be expensive on some platforms, and the -minimum allocation length may be as big as a page, so you should -consolidate your requests for consistent memory as much as possible. -The simplest way to do that is to use the dma_pool calls (see below). - -The flag parameter (dma_alloc_coherent() only) allows the caller to -specify the ``GFP_`` flags (see kmalloc()) for the allocation (the -implementation may choose to ignore flags that affect the location of -the returned memory, like GFP_DMA). - -:: - - void - dma_free_coherent(struct device *dev, size_t size, void *cpu_addr, - dma_addr_t dma_handle) - -Free a region of consistent memory you previously allocated. dev, -size and dma_handle must all be the same as those passed into -dma_alloc_coherent(). cpu_addr must be the virtual address returned by -the dma_alloc_coherent(). - -Note that unlike their sibling allocation calls, these routines -may only be called with IRQs enabled. - - -Part Ib - Using small DMA-coherent buffers ------------------------------------------- - -To get this part of the dma_API, you must #include <linux/dmapool.h> - -Many drivers need lots of small DMA-coherent memory regions for DMA -descriptors or I/O buffers. Rather than allocating in units of a page -or more using dma_alloc_coherent(), you can use DMA pools. These work -much like a struct kmem_cache, except that they use the DMA-coherent allocator, -not __get_free_pages(). Also, they understand common hardware constraints -for alignment, like queue heads needing to be aligned on N-byte boundaries. - - -:: - - struct dma_pool * - dma_pool_create(const char *name, struct device *dev, - size_t size, size_t align, size_t alloc); - -dma_pool_create() initializes a pool of DMA-coherent buffers -for use with a given device. It must be called in a context which -can sleep. - -The "name" is for diagnostics (like a struct kmem_cache name); dev and size -are like what you'd pass to dma_alloc_coherent(). The device's hardware -alignment requirement for this type of data is "align" (which is expressed -in bytes, and must be a power of two). If your device has no boundary -crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated -from this pool must not cross 4KByte boundaries. - -:: - - void * - dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags, - dma_addr_t *handle) - -Wraps dma_pool_alloc() and also zeroes the returned memory if the -allocation attempt succeeded. - - -:: - - void * - dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags, - dma_addr_t *dma_handle); - -This allocates memory from the pool; the returned memory will meet the -size and alignment requirements specified at creation time. Pass -GFP_ATOMIC to prevent blocking, or if it's permitted (not -in_interrupt, not holding SMP locks), pass GFP_KERNEL to allow -blocking. Like dma_alloc_coherent(), this returns two values: an -address usable by the CPU, and the DMA address usable by the pool's -device. - -:: - - void - dma_pool_free(struct dma_pool *pool, void *vaddr, - dma_addr_t addr); - -This puts memory back into the pool. The pool is what was passed to -dma_pool_alloc(); the CPU (vaddr) and DMA addresses are what -were returned when that routine allocated the memory being freed. - -:: - - void - dma_pool_destroy(struct dma_pool *pool); - -dma_pool_destroy() frees the resources of the pool. It must be -called in a context which can sleep. Make sure you've freed all allocated -memory back to the pool before you destroy it. - - -Part Ic - DMA addressing limitations ------------------------------------- - -:: - - int - dma_set_mask_and_coherent(struct device *dev, u64 mask) - -Checks to see if the mask is possible and updates the device -streaming and coherent DMA mask parameters if it is. - -Returns: 0 if successful and a negative error if not. - -:: - - int - dma_set_mask(struct device *dev, u64 mask) - -Checks to see if the mask is possible and updates the device -parameters if it is. - -Returns: 0 if successful and a negative error if not. - -:: - - int - dma_set_coherent_mask(struct device *dev, u64 mask) - -Checks to see if the mask is possible and updates the device -parameters if it is. - -Returns: 0 if successful and a negative error if not. - -:: - - u64 - dma_get_required_mask(struct device *dev) - -This API returns the mask that the platform requires to -operate efficiently. Usually this means the returned mask -is the minimum required to cover all of memory. Examining the -required mask gives drivers with variable descriptor sizes the -opportunity to use smaller descriptors as necessary. - -Requesting the required mask does not alter the current mask. If you -wish to take advantage of it, you should issue a dma_set_mask() -call to set the mask to the value returned. - -:: - - size_t - dma_max_mapping_size(struct device *dev); - -Returns the maximum size of a mapping for the device. The size parameter -of the mapping functions like dma_map_single(), dma_map_page() and -others should not be larger than the returned value. - -:: - - unsigned long - dma_get_merge_boundary(struct device *dev); - -Returns the DMA merge boundary. If the device cannot merge any the DMA address -segments, the function returns 0. - -Part Id - Streaming DMA mappings --------------------------------- - -:: - - dma_addr_t - dma_map_single(struct device *dev, void *cpu_addr, size_t size, - enum dma_data_direction direction) - -Maps a piece of processor virtual memory so it can be accessed by the -device and returns the DMA address of the memory. - -The direction for both APIs may be converted freely by casting. -However the dma_API uses a strongly typed enumerator for its -direction: - -======================= ============================================= -DMA_NONE no direction (used for debugging) -DMA_TO_DEVICE data is going from the memory to the device -DMA_FROM_DEVICE data is coming from the device to the memory -DMA_BIDIRECTIONAL direction isn't known -======================= ============================================= - -.. note:: - - Not all memory regions in a machine can be mapped by this API. - Further, contiguous kernel virtual space may not be contiguous as - physical memory. Since this API does not provide any scatter/gather - capability, it will fail if the user tries to map a non-physically - contiguous piece of memory. For this reason, memory to be mapped by - this API should be obtained from sources which guarantee it to be - physically contiguous (like kmalloc). - - Further, the DMA address of the memory must be within the - dma_mask of the device (the dma_mask is a bit mask of the - addressable region for the device, i.e., if the DMA address of - the memory ANDed with the dma_mask is still equal to the DMA - address, then the device can perform DMA to the memory). To - ensure that the memory allocated by kmalloc is within the dma_mask, - the driver may specify various platform-dependent flags to restrict - the DMA address range of the allocation (e.g., on x86, GFP_DMA - guarantees to be within the first 16MB of available DMA addresses, - as required by ISA devices). - - Note also that the above constraints on physical contiguity and - dma_mask may not apply if the platform has an IOMMU (a device which - maps an I/O DMA address to a physical memory address). However, to be - portable, device driver writers may *not* assume that such an IOMMU - exists. - -.. warning:: - - Memory coherency operates at a granularity called the cache - line width. In order for memory mapped by this API to operate - correctly, the mapped region must begin exactly on a cache line - boundary and end exactly on one (to prevent two separately mapped - regions from sharing a single cache line). Since the cache line size - may not be known at compile time, the API will not enforce this - requirement. Therefore, it is recommended that driver writers who - don't take special care to determine the cache line size at run time - only map virtual regions that begin and end on page boundaries (which - are guaranteed also to be cache line boundaries). - - DMA_TO_DEVICE synchronisation must be done after the last modification - of the memory region by the software and before it is handed off to - the device. Once this primitive is used, memory covered by this - primitive should be treated as read-only by the device. If the device - may write to it at any point, it should be DMA_BIDIRECTIONAL (see - below). - - DMA_FROM_DEVICE synchronisation must be done before the driver - accesses data that may be changed by the device. This memory should - be treated as read-only by the driver. If the driver needs to write - to it at any point, it should be DMA_BIDIRECTIONAL (see below). - - DMA_BIDIRECTIONAL requires special handling: it means that the driver - isn't sure if the memory was modified before being handed off to the - device and also isn't sure if the device will also modify it. Thus, - you must always sync bidirectional memory twice: once before the - memory is handed off to the device (to make sure all memory changes - are flushed from the processor) and once before the data may be - accessed after being used by the device (to make sure any processor - cache lines are updated with data that the device may have changed). - -:: - - void - dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size, - enum dma_data_direction direction) - -Unmaps the region previously mapped. All the parameters passed in -must be identical to those passed in (and returned) by the mapping -API. - -:: - - dma_addr_t - dma_map_page(struct device *dev, struct page *page, - unsigned long offset, size_t size, - enum dma_data_direction direction) - - void - dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size, - enum dma_data_direction direction) - -API for mapping and unmapping for pages. All the notes and warnings -for the other mapping APIs apply here. Also, although the <offset> -and <size> parameters are provided to do partial page mapping, it is -recommended that you never use these unless you really know what the -cache width is. - -:: - - dma_addr_t - dma_map_resource(struct device *dev, phys_addr_t phys_addr, size_t size, - enum dma_data_direction dir, unsigned long attrs) - - void - dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size, - enum dma_data_direction dir, unsigned long attrs) - -API for mapping and unmapping for MMIO resources. All the notes and -warnings for the other mapping APIs apply here. The API should only be -used to map device MMIO resources, mapping of RAM is not permitted. - -:: - - int - dma_mapping_error(struct device *dev, dma_addr_t dma_addr) - -In some circumstances dma_map_single(), dma_map_page() and dma_map_resource() -will fail to create a mapping. A driver can check for these errors by testing -the returned DMA address with dma_mapping_error(). A non-zero return value -means the mapping could not be created and the driver should take appropriate -action (e.g. reduce current DMA mapping usage or delay and try again later). - -:: - - int - dma_map_sg(struct device *dev, struct scatterlist *sg, - int nents, enum dma_data_direction direction) - -Returns: the number of DMA address segments mapped (this may be shorter -than <nents> passed in if some elements of the scatter/gather list are -physically or virtually adjacent and an IOMMU maps them with a single -entry). - -Please note that the sg cannot be mapped again if it has been mapped once. -The mapping process is allowed to destroy information in the sg. - -As with the other mapping interfaces, dma_map_sg() can fail. When it -does, 0 is returned and a driver must take appropriate action. It is -critical that the driver do something, in the case of a block driver -aborting the request or even oopsing is better than doing nothing and -corrupting the filesystem. - -With scatterlists, you use the resulting mapping like this:: - - int i, count = dma_map_sg(dev, sglist, nents, direction); - struct scatterlist *sg; - - for_each_sg(sglist, sg, count, i) { - hw_address[i] = sg_dma_address(sg); - hw_len[i] = sg_dma_len(sg); - } - -where nents is the number of entries in the sglist. - -The implementation is free to merge several consecutive sglist entries -into one (e.g. with an IOMMU, or if several pages just happen to be -physically contiguous) and returns the actual number of sg entries it -mapped them to. On failure 0, is returned. - -Then you should loop count times (note: this can be less than nents times) -and use sg_dma_address() and sg_dma_len() macros where you previously -accessed sg->address and sg->length as shown above. - -:: - - void - dma_unmap_sg(struct device *dev, struct scatterlist *sg, - int nents, enum dma_data_direction direction) - -Unmap the previously mapped scatter/gather list. All the parameters -must be the same as those and passed in to the scatter/gather mapping -API. - -Note: <nents> must be the number you passed in, *not* the number of -DMA address entries returned. - -:: - - void - dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, - size_t size, - enum dma_data_direction direction) - - void - dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, - size_t size, - enum dma_data_direction direction) - - void - dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, - int nents, - enum dma_data_direction direction) - - void - dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, - int nents, - enum dma_data_direction direction) - -Synchronise a single contiguous or scatter/gather mapping for the CPU -and device. With the sync_sg API, all the parameters must be the same -as those passed into the single mapping API. With the sync_single API, -you can use dma_handle and size parameters that aren't identical to -those passed into the single mapping API to do a partial sync. - - -.. note:: - - You must do this: - - - Before reading values that have been written by DMA from the device - (use the DMA_FROM_DEVICE direction) - - After writing values that will be written to the device using DMA - (use the DMA_TO_DEVICE) direction - - before *and* after handing memory to the device if the memory is - DMA_BIDIRECTIONAL - -See also dma_map_single(). - -:: - - dma_addr_t - dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size, - enum dma_data_direction dir, - unsigned long attrs) - - void - dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr, - size_t size, enum dma_data_direction dir, - unsigned long attrs) - - int - dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl, - int nents, enum dma_data_direction dir, - unsigned long attrs) - - void - dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl, - int nents, enum dma_data_direction dir, - unsigned long attrs) - -The four functions above are just like the counterpart functions -without the _attrs suffixes, except that they pass an optional -dma_attrs. - -The interpretation of DMA attributes is architecture-specific, and -each attribute should be documented in Documentation/DMA-attributes.txt. - -If dma_attrs are 0, the semantics of each of these functions -is identical to those of the corresponding function -without the _attrs suffix. As a result dma_map_single_attrs() -can generally replace dma_map_single(), etc. - -As an example of the use of the ``*_attrs`` functions, here's how -you could pass an attribute DMA_ATTR_FOO when mapping memory -for DMA:: - - #include <linux/dma-mapping.h> - /* DMA_ATTR_FOO should be defined in linux/dma-mapping.h and - * documented in Documentation/DMA-attributes.txt */ - ... - - unsigned long attr; - attr |= DMA_ATTR_FOO; - .... - n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, attr); - .... - -Architectures that care about DMA_ATTR_FOO would check for its -presence in their implementations of the mapping and unmapping -routines, e.g.::: - - void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr, - size_t size, enum dma_data_direction dir, - unsigned long attrs) - { - .... - if (attrs & DMA_ATTR_FOO) - /* twizzle the frobnozzle */ - .... - } - - -Part II - Advanced dma usage ----------------------------- - -Warning: These pieces of the DMA API should not be used in the -majority of cases, since they cater for unlikely corner cases that -don't belong in usual drivers. - -If you don't understand how cache line coherency works between a -processor and an I/O device, you should not be using this part of the -API at all. - -:: - - void * - dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle, - gfp_t flag, unsigned long attrs) - -Identical to dma_alloc_coherent() except that when the -DMA_ATTR_NON_CONSISTENT flags is passed in the attrs argument, the -platform will choose to return either consistent or non-consistent memory -as it sees fit. By using this API, you are guaranteeing to the platform -that you have all the correct and necessary sync points for this memory -in the driver should it choose to return non-consistent memory. - -Note: where the platform can return consistent memory, it will -guarantee that the sync points become nops. - -Warning: Handling non-consistent memory is a real pain. You should -only use this API if you positively know your driver will be -required to work on one of the rare (usually non-PCI) architectures -that simply cannot make consistent memory. - -:: - - void - dma_free_attrs(struct device *dev, size_t size, void *cpu_addr, - dma_addr_t dma_handle, unsigned long attrs) - -Free memory allocated by the dma_alloc_attrs(). All common -parameters must be identical to those otherwise passed to dma_free_coherent, -and the attrs argument must be identical to the attrs passed to -dma_alloc_attrs(). - -:: - - int - dma_get_cache_alignment(void) - -Returns the processor cache alignment. This is the absolute minimum -alignment *and* width that you must observe when either mapping -memory or doing partial flushes. - -.. note:: - - This API may return a number *larger* than the actual cache - line, but it will guarantee that one or more cache lines fit exactly - into the width returned by this call. It will also always be a power - of two for easy alignment. - -:: - - void - dma_cache_sync(struct device *dev, void *vaddr, size_t size, - enum dma_data_direction direction) - -Do a partial sync of memory that was allocated by dma_alloc_attrs() with -the DMA_ATTR_NON_CONSISTENT flag starting at virtual address vaddr and -continuing on for size. Again, you *must* observe the cache line -boundaries when doing this. - -:: - - int - dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr, - dma_addr_t device_addr, size_t size); - -Declare region of memory to be handed out by dma_alloc_coherent() when -it's asked for coherent memory for this device. - -phys_addr is the CPU physical address to which the memory is currently -assigned (this will be ioremapped so the CPU can access the region). - -device_addr is the DMA address the device needs to be programmed -with to actually address this memory (this will be handed out as the -dma_addr_t in dma_alloc_coherent()). - -size is the size of the area (must be multiples of PAGE_SIZE). - -As a simplification for the platforms, only *one* such region of -memory may be declared per device. - -For reasons of efficiency, most platforms choose to track the declared -region only at the granularity of a page. For smaller allocations, -you should use the dma_pool() API. - -Part III - Debug drivers use of the DMA-API -------------------------------------------- - -The DMA-API as described above has some constraints. DMA addresses must be -released with the corresponding function with the same size for example. With -the advent of hardware IOMMUs it becomes more and more important that drivers -do not violate those constraints. In the worst case such a violation can -result in data corruption up to destroyed filesystems. - -To debug drivers and find bugs in the usage of the DMA-API checking code can -be compiled into the kernel which will tell the developer about those -violations. If your architecture supports it you can select the "Enable -debugging of DMA-API usage" option in your kernel configuration. Enabling this -option has a performance impact. Do not enable it in production kernels. - -If you boot the resulting kernel will contain code which does some bookkeeping -about what DMA memory was allocated for which device. If this code detects an -error it prints a warning message with some details into your kernel log. An -example warning message may look like this:: - - WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448 - check_unmap+0x203/0x490() - Hardware name: - forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong - function [device address=0x00000000640444be] [size=66 bytes] [mapped as - single] [unmapped as page] - Modules linked in: nfsd exportfs bridge stp llc r8169 - Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1 - Call Trace: - <IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130 - [<ffffffff80647b70>] _spin_unlock+0x10/0x30 - [<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0 - [<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40 - [<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0 - [<ffffffff80252f96>] queue_work+0x56/0x60 - [<ffffffff80237e10>] enqueue_task_fair+0x20/0x50 - [<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0 - [<ffffffff803b78c3>] cpumask_next_and+0x23/0x40 - [<ffffffff80235177>] find_busiest_group+0x207/0x8a0 - [<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50 - [<ffffffff803c7ea3>] check_unmap+0x203/0x490 - [<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50 - [<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0 - [<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0 - [<ffffffff8026df84>] handle_IRQ_event+0x34/0x70 - [<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150 - [<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0 - [<ffffffff8020c093>] ret_from_intr+0x0/0xa - <EOI> <4>---[ end trace f6435a98e2a38c0e ]--- - -The driver developer can find the driver and the device including a stacktrace -of the DMA-API call which caused this warning. - -Per default only the first error will result in a warning message. All other -errors will only silently counted. This limitation exist to prevent the code -from flooding your kernel log. To support debugging a device driver this can -be disabled via debugfs. See the debugfs interface documentation below for -details. - -The debugfs directory for the DMA-API debugging code is called dma-api/. In -this directory the following files can currently be found: - -=============================== =============================================== -dma-api/all_errors This file contains a numeric value. If this - value is not equal to zero the debugging code - will print a warning for every error it finds - into the kernel log. Be careful with this - option, as it can easily flood your logs. - -dma-api/disabled This read-only file contains the character 'Y' - if the debugging code is disabled. This can - happen when it runs out of memory or if it was - disabled at boot time - -dma-api/dump This read-only file contains current DMA - mappings. - -dma-api/error_count This file is read-only and shows the total - numbers of errors found. - -dma-api/num_errors The number in this file shows how many - warnings will be printed to the kernel log - before it stops. This number is initialized to - one at system boot and be set by writing into - this file - -dma-api/min_free_entries This read-only file can be read to get the - minimum number of free dma_debug_entries the - allocator has ever seen. If this value goes - down to zero the code will attempt to increase - nr_total_entries to compensate. - -dma-api/num_free_entries The current number of free dma_debug_entries - in the allocator. - -dma-api/nr_total_entries The total number of dma_debug_entries in the - allocator, both free and used. - -dma-api/driver_filter You can write a name of a driver into this file - to limit the debug output to requests from that - particular driver. Write an empty string to - that file to disable the filter and see - all errors again. -=============================== =============================================== - -If you have this code compiled into your kernel it will be enabled by default. -If you want to boot without the bookkeeping anyway you can provide -'dma_debug=off' as a boot parameter. This will disable DMA-API debugging. -Notice that you can not enable it again at runtime. You have to reboot to do -so. - -If you want to see debug messages only for a special device driver you can -specify the dma_debug_driver=<drivername> parameter. This will enable the -driver filter at boot time. The debug code will only print errors for that -driver afterwards. This filter can be disabled or changed later using debugfs. - -When the code disables itself at runtime this is most likely because it ran -out of dma_debug_entries and was unable to allocate more on-demand. 65536 -entries are preallocated at boot - if this is too low for you boot with -'dma_debug_entries=<your_desired_number>' to overwrite the default. Note -that the code allocates entries in batches, so the exact number of -preallocated entries may be greater than the actual number requested. The -code will print to the kernel log each time it has dynamically allocated -as many entries as were initially preallocated. This is to indicate that a -larger preallocation size may be appropriate, or if it happens continually -that a driver may be leaking mappings. - -:: - - void - debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr); - -dma-debug interface debug_dma_mapping_error() to debug drivers that fail -to check DMA mapping errors on addresses returned by dma_map_single() and -dma_map_page() interfaces. This interface clears a flag set by -debug_dma_map_page() to indicate that dma_mapping_error() has been called by -the driver. When driver does unmap, debug_dma_unmap() checks the flag and if -this flag is still set, prints warning message that includes call trace that -leads up to the unmap. This interface can be called from dma_mapping_error() -routines to enable DMA mapping error check debugging. |