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@@ -83,3 +83,114 @@ The meta-intel maintainers will do their best to review and/or pull in a patch or patchset within 24 hours of the time it was posted. For larger and/or more involved patches and patchsets, the review process may take longer. + + +Intel-specific machine features +=============================== + +The meta-intel layer makes some additional machine features available +to BSPs. These machine features can be used in a BSP layer in the +same way that machine features are used in other layers based on +oe-core, via the MACHINE_FEATURES variable. + +Requirements +------------ + +The meta-intel-specific machine features are only available to a BSP +when the meta-intel layer is included in the build configuration, and +the meta-intel.inc file is included in the machine configuration of +that BSP. + +To make these features available for your machine, you will need to: + + 1. include a configuration line such as the below in bblayers.conf + BBLAYERS += "<local path>/meta-intel" + 2. include the following line in the machine configuration file + require conf/machine/include/meta-intel.inc + +Once the above requirements are met, the machine features provided by +the meta-intel layer will be available for the BSP to use. + +Available machine features +-------------------------- + +Currently, the meta-intel layer makes the following set of +Intel-specific machine features available: + + * intel-ucode + +These machine features can be included by listing them in the +MACHINE_FEATURES variable in the machine configuration file. For +example: + + MACHINE_FEATURES += "intel-ucode" + +Machine feature details +----------------------- + + * intel-ucode + + This feature provides support for microcode updates to Intel + processors. The intel-ucode feature runs at early boot and uses + the microcode data file added by the feature into the BSP's + initrd. It also puts the userland microcode-updating tool, + iucode_tool, into the target images along with the microcode data + file. + + Q. Why might a user want to enable the intel-ucode feature? + + A. Intel releases microcode updates to correct processor behavior + as documented in the respective processor specification + updates. While the normal approach to getting such microcode + updates is via a BIOS upgrade, this can be an administrative + hassle and not always possible in the field. The intel-ucode + feature enables the microcode update capability present in the + Linux kernel. It provides an easy path for upgrading processor + microcode without the need to change the BIOS. If the feature + is enabled, it is also possible to update the existing target + images with a newer microcode update in the future. + + Q. How would a user bundle only target-specific microcode in the + target image? + + A. The Intel microcode data file released by Intel contains + microcode updates for multiple processors. If the BSP image is + meant to run on only a certain subset of processor types, a + processor-specific subset of microcode can be bundled into the + target image via the UCODE_FILTER_PARAMETERS variable. This + works by listing a sequence of iucode-tool parameters in the + UCODE_FILTER_PARAMETERS variable, which in this case will + select only the specific microcode relevant to the BSP. For + more information on the underlying parameters refer to the + iucode-tool manual page at http://manned.org/iucode-tool + + To define a set of parameters for microcode-filtering via the + UCODE_FILTER_PARAMETERS variable, one needs to identify the + cpuid signatures of all the processors the BSP is meant to run + on. One way to determine the cpuid signature for a specific + processor is to build and run an intel-ucode-feature-enabled + image on the target hardware, without first assigning any value + to the UCODE_FILTER_PARAMETERS variable, and then once the + image is booted, run the "ucode_tool -S" command to have the + ucode tool scan the system for processor signatures. These + signatures can then be used in the UCODE_FILTER_PARAMETERS + variable in conjunction with -s parameter. For example, for + the fri2 BSP, the cpuid can be determined as such: + + [root@fri2 ~]# iucode_tool -S + iucode_tool: system has processor(s) with signature 0x00020661 + + Given that output, a suitable UCODE_FILTER_PARAMETERS variable + definition could be specified in the machine configuration as + such: + + UCODE_FILTER_PARAMETERS = "-s 0x00020661" + + Q. Are there any reasons a user might want to disable the + intel-ucode feature? + + A. The microcode data file and associated tools occupy a small + amount of space (a few KB) on the target image. BSPs which are + highly sensitive to target image size and which are not + experiencing microcode-related issues might consider not + enabling this feature. |