€•C)      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ-/translations/zh_CN/arch/powerpc/cpu_features”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/zh_TW/arch/powerpc/cpu_features”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/it_IT/arch/powerpc/cpu_features”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/ja_JP/arch/powerpc/cpu_features”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/ko_KR/arch/powerpc/cpu_features”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/sp_SP/arch/powerpc/cpu_features”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒCPU Features”h]”hŒCPU Features”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒG/var/lib/git/docbuild/linux/Documentation/arch/powerpc/cpu_features.rst”h KubhŒ	paragraph”“”)”}”(hŒ3Hollis Blanchard <hollis@austin.ibm.com>
5 Jun 2002”h]”(hŒHollis Blanchard <”…””}”(hh¹hžhhŸNh NubhŒ	reference”“”)”}”(hŒhollis@austin.ibm.com”h]”hŒhollis@austin.ibm.com”…””}”(hhÃhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”Œmailto:hollis@austin.ibm.com”uh1hÁhh¹ubhŒ>
5 Jun 2002”…””}”(hh¹hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒ®This document describes the system (including self-modifying code) used in the
PPC Linux kernel to support a variety of PowerPC CPUs without requiring
compile-time selection.”h]”hŒ®This document describes the system (including self-modifying code) used in the
PPC Linux kernel to support a variety of PowerPC CPUs without requiring
compile-time selection.”…””}”(hhÝhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒòEarly in the boot process the ppc32 kernel detects the current CPU type and
chooses a set of features accordingly. Some examples include Altivec support,
split instruction and data caches, and if the CPU supports the DOZE and NAP
sleep modes.”h]”hŒòEarly in the boot process the ppc32 kernel detects the current CPU type and
chooses a set of features accordingly. Some examples include Altivec support,
split instruction and data caches, and if the CPU supports the DOZE and NAP
sleep modes.”…””}”(hhëhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hXC  Detection of the feature set is simple. A list of processors can be found in
arch/powerpc/kernel/cputable.c. The PVR register is masked and compared with
each value in the list. If a match is found, the cpu_features of cur_cpu_spec
is assigned to the feature bitmask for this processor and a __setup_cpu
function is called.”h]”hXC  Detection of the feature set is simple. A list of processors can be found in
arch/powerpc/kernel/cputable.c. The PVR register is masked and compared with
each value in the list. If a match is found, the cpu_features of cur_cpu_spec
is assigned to the feature bitmask for this processor and a __setup_cpu
function is called.”…””}”(hhùhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒ£C code may test 'cur_cpu_spec[smp_processor_id()]->cpu_features' for a
particular feature bit. This is done in quite a few places, for example
in ppc_setup_l2cr().”h]”hŒ§C code may test â€˜cur_cpu_spec[smp_processor_id()]->cpu_featuresâ€™ for a
particular feature bit. This is done in quite a few places, for example
in ppc_setup_l2cr().”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hX  Implementing cpufeatures in assembly is a little more involved. There are
several paths that are performance-critical and would suffer if an array
index, structure dereference, and conditional branch were added. To avoid the
performance penalty but still allow for runtime (rather than compile-time) CPU
selection, unused code is replaced by 'nop' instructions. This nop'ing is
based on CPU 0's capabilities, so a multi-processor system with non-identical
processors will not work (but such a system would likely have other problems
anyways).”h]”hX&  Implementing cpufeatures in assembly is a little more involved. There are
several paths that are performance-critical and would suffer if an array
index, structure dereference, and conditional branch were added. To avoid the
performance penalty but still allow for runtime (rather than compile-time) CPU
selection, unused code is replaced by â€˜nopâ€™ instructions. This nopâ€™ing is
based on CPU 0â€™s capabilities, so a multi-processor system with non-identical
processors will not work (but such a system would likely have other problems
anyways).”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒýAfter detecting the processor type, the kernel patches out sections of code
that shouldn't be used by writing nop's over it. Using cpufeatures requires
just 2 macros (found in arch/powerpc/include/asm/cputable.h), as seen in head.S
transfer_to_handler::”h]”hX   After detecting the processor type, the kernel patches out sections of code
that shouldnâ€™t be used by writing nopâ€™s over it. Using cpufeatures requires
just 2 macros (found in arch/powerpc/include/asm/cputable.h), as seen in head.S
transfer_to_handler:”…””}”(hj#  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K$hh£hžhubhŒliteral_block”“”)”}”(hŒá#ifdef CONFIG_ALTIVEC
BEGIN_FTR_SECTION
        mfspr   r22,SPRN_VRSAVE         /* if G4, save vrsave register value */
        stw     r22,THREAD_VRSAVE(r23)
END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
#endif /* CONFIG_ALTIVEC */”h]”hŒá#ifdef CONFIG_ALTIVEC
BEGIN_FTR_SECTION
        mfspr   r22,SPRN_VRSAVE         /* if G4, save vrsave register value */
        stw     r22,THREAD_VRSAVE(r23)
END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
#endif /* CONFIG_ALTIVEC */”…””}”hj3  sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1j1  hŸh¶h K)hh£hžhubh¸)”}”(hŒpIf CPU 0 supports Altivec, the code is left untouched. If it doesn't, both
instructions are replaced with nop's.”h]”hŒtIf CPU 0 supports Altivec, the code is left untouched. If it doesnâ€™t, both
instructions are replaced with nopâ€™s.”…””}”(hjC  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K0hh£hžhubh¸)”}”(hX  The END_FTR_SECTION macro has two simpler variations: END_FTR_SECTION_IFSET
and END_FTR_SECTION_IFCLR. These simply test if a flag is set (in
cur_cpu_spec[0]->cpu_features) or is cleared, respectively. These two macros
should be used in the majority of cases.”h]”hX  The END_FTR_SECTION macro has two simpler variations: END_FTR_SECTION_IFSET
and END_FTR_SECTION_IFCLR. These simply test if a flag is set (in
cur_cpu_spec[0]->cpu_features) or is cleared, respectively. These two macros
should be used in the majority of cases.”…””}”(hjQ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K3hh£hžhubh¸)”}”(hXZ  The END_FTR_SECTION macros are implemented by storing information about this
code in the '__ftr_fixup' ELF section. When do_cpu_ftr_fixups
(arch/powerpc/kernel/misc.S) is invoked, it will iterate over the records in
__ftr_fixup, and if the required feature is not present it will loop writing
nop's from each BEGIN_FTR_SECTION to END_FTR_SECTION.”h]”hX`  The END_FTR_SECTION macros are implemented by storing information about this
code in the â€˜__ftr_fixupâ€™ ELF section. When do_cpu_ftr_fixups
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