diff options
Diffstat (limited to 'README')
-rw-r--r-- | README | 111 |
1 files changed, 111 insertions, 0 deletions
@@ -83,3 +83,114 @@ The meta-intel maintainers will do their best to review and/or pull in | |||
83 | a patch or patchset within 24 hours of the time it was posted. For | 83 | a patch or patchset within 24 hours of the time it was posted. For |
84 | larger and/or more involved patches and patchsets, the review process | 84 | larger and/or more involved patches and patchsets, the review process |
85 | may take longer. | 85 | may take longer. |
86 | |||
87 | |||
88 | Intel-specific machine features | ||
89 | =============================== | ||
90 | |||
91 | The meta-intel layer makes some additional machine features available | ||
92 | to BSPs. These machine features can be used in a BSP layer in the | ||
93 | same way that machine features are used in other layers based on | ||
94 | oe-core, via the MACHINE_FEATURES variable. | ||
95 | |||
96 | Requirements | ||
97 | ------------ | ||
98 | |||
99 | The meta-intel-specific machine features are only available to a BSP | ||
100 | when the meta-intel layer is included in the build configuration, and | ||
101 | the meta-intel.inc file is included in the machine configuration of | ||
102 | that BSP. | ||
103 | |||
104 | To make these features available for your machine, you will need to: | ||
105 | |||
106 | 1. include a configuration line such as the below in bblayers.conf | ||
107 | BBLAYERS += "<local path>/meta-intel" | ||
108 | 2. include the following line in the machine configuration file | ||
109 | require conf/machine/include/meta-intel.inc | ||
110 | |||
111 | Once the above requirements are met, the machine features provided by | ||
112 | the meta-intel layer will be available for the BSP to use. | ||
113 | |||
114 | Available machine features | ||
115 | -------------------------- | ||
116 | |||
117 | Currently, the meta-intel layer makes the following set of | ||
118 | Intel-specific machine features available: | ||
119 | |||
120 | * intel-ucode | ||
121 | |||
122 | These machine features can be included by listing them in the | ||
123 | MACHINE_FEATURES variable in the machine configuration file. For | ||
124 | example: | ||
125 | |||
126 | MACHINE_FEATURES += "intel-ucode" | ||
127 | |||
128 | Machine feature details | ||
129 | ----------------------- | ||
130 | |||
131 | * intel-ucode | ||
132 | |||
133 | This feature provides support for microcode updates to Intel | ||
134 | processors. The intel-ucode feature runs at early boot and uses | ||
135 | the microcode data file added by the feature into the BSP's | ||
136 | initrd. It also puts the userland microcode-updating tool, | ||
137 | iucode_tool, into the target images along with the microcode data | ||
138 | file. | ||
139 | |||
140 | Q. Why might a user want to enable the intel-ucode feature? | ||
141 | |||
142 | A. Intel releases microcode updates to correct processor behavior | ||
143 | as documented in the respective processor specification | ||
144 | updates. While the normal approach to getting such microcode | ||
145 | updates is via a BIOS upgrade, this can be an administrative | ||
146 | hassle and not always possible in the field. The intel-ucode | ||
147 | feature enables the microcode update capability present in the | ||
148 | Linux kernel. It provides an easy path for upgrading processor | ||
149 | microcode without the need to change the BIOS. If the feature | ||
150 | is enabled, it is also possible to update the existing target | ||
151 | images with a newer microcode update in the future. | ||
152 | |||
153 | Q. How would a user bundle only target-specific microcode in the | ||
154 | target image? | ||
155 | |||
156 | A. The Intel microcode data file released by Intel contains | ||
157 | microcode updates for multiple processors. If the BSP image is | ||
158 | meant to run on only a certain subset of processor types, a | ||
159 | processor-specific subset of microcode can be bundled into the | ||
160 | target image via the UCODE_FILTER_PARAMETERS variable. This | ||
161 | works by listing a sequence of iucode-tool parameters in the | ||
162 | UCODE_FILTER_PARAMETERS variable, which in this case will | ||
163 | select only the specific microcode relevant to the BSP. For | ||
164 | more information on the underlying parameters refer to the | ||
165 | iucode-tool manual page at http://manned.org/iucode-tool | ||
166 | |||
167 | To define a set of parameters for microcode-filtering via the | ||
168 | UCODE_FILTER_PARAMETERS variable, one needs to identify the | ||
169 | cpuid signatures of all the processors the BSP is meant to run | ||
170 | on. One way to determine the cpuid signature for a specific | ||
171 | processor is to build and run an intel-ucode-feature-enabled | ||
172 | image on the target hardware, without first assigning any value | ||
173 | to the UCODE_FILTER_PARAMETERS variable, and then once the | ||
174 | image is booted, run the "ucode_tool -S" command to have the | ||
175 | ucode tool scan the system for processor signatures. These | ||
176 | signatures can then be used in the UCODE_FILTER_PARAMETERS | ||
177 | variable in conjunction with -s parameter. For example, for | ||
178 | the fri2 BSP, the cpuid can be determined as such: | ||
179 | |||
180 | [root@fri2 ~]# iucode_tool -S | ||
181 | iucode_tool: system has processor(s) with signature 0x00020661 | ||
182 | |||
183 | Given that output, a suitable UCODE_FILTER_PARAMETERS variable | ||
184 | definition could be specified in the machine configuration as | ||
185 | such: | ||
186 | |||
187 | UCODE_FILTER_PARAMETERS = "-s 0x00020661" | ||
188 | |||
189 | Q. Are there any reasons a user might want to disable the | ||
190 | intel-ucode feature? | ||
191 | |||
192 | A. The microcode data file and associated tools occupy a small | ||
193 | amount of space (a few KB) on the target image. BSPs which are | ||
194 | highly sensitive to target image size and which are not | ||
195 | experiencing microcode-related issues might consider not | ||
196 | enabling this feature. | ||