[PATCH] ARM: Add writethrough dcache support for ARM926EJS processor

[Sergei Shtylyov]

Hello.

I wrote:

>> From: Mark A. Greer <mgreer at mvista.com>

>> The ARM kernel supports writethrough data cache via the
>> CONFIG_CPU_DCACHE_WRITETHROUGH option.  However, that
>> functionality wasn't implemented in the arch/arm/boot/compressed
>> code.  It is now necessary due to a new ARM926EJS processor
>> that has an issue with writeback data cache.

>> Signed-off-by: Mark A. Greer <mgreer at mvista.com>
>> ---
>> This patch was motivated by a dcache writeback bug in some revisions
>> of TI's DA830/OMAP-L137 (ARM926EJS) SoC.  It has been tested using
>> Kevin Hilman's DaVinci tree where that SoC is supported.  Compile
>> tested only in the linux-2.6 ARM kernel.

>> I submitted this patch a while back,
>>     http://marc.info/?l=linux-arm-kernel&m=124208189923479&w=4
>> and Russell responded with,
>>     http://marc.info/?l=linux-arm-kernel&m=124277262417440&w=4
>> to which both George Davis and I responded but Russell has been too
>> busy to continue the conversation.

>> So, I'm resubmitting in the hope that this patch gets accepted or I
>> can get some more feedback as to what needs to be done to make it
>> acceptable.

>> Many thanks to George Davis for helping me with the low-level ARM-ese.

>>  arch/arm/boot/compressed/head.S |   16 ++++++++++++++++
>>  1 files changed, 16 insertions(+), 0 deletions(-)

>> diff --git a/arch/arm/boot/compressed/head.S 
>> b/arch/arm/boot/compressed/head.S
>> index fa6fbf4..70806c1 100644
>> --- a/arch/arm/boot/compressed/head.S
>> +++ b/arch/arm/boot/compressed/head.S
>> @@ -412,7 +412,11 @@ __setup_mmu:    sub    r3, r4, #16384        @ 
>> Page directory size
>>          orr    r1, r1, #3 << 10
>>          add    r2, r3, #16384
>>  1:        cmp    r1, r9            @ if virt > start of RAM
>> +#ifdef CONFIG_CPU_DCACHE_WRITETHROUGH
>> +        orrhs    r1, r1, #0x08        @ set cacheable
>> +#else
>>          orrhs    r1, r1, #0x0c        @ set cacheable, bufferable
>> +#endif
>>          cmp    r1, r10            @ if virt > end of RAM
>>          bichs    r1, r1, #0x0c        @ clear cacheable, bufferable
>>          str    r1, [r0], #4        @ 1:1 mapping
>> @@ -436,6 +440,12 @@ __setup_mmu:    sub    r3, r4, #16384        @ 
>> Page directory size
>>          mov    pc, lr
>>  ENDPROC(__setup_mmu)
>>  
>> +__arm926ejs_mmu_cache_on:
>> +#ifdef CONFIG_CPU_DCACHE_WRITETHROUGH
>> +        mov    r0, #4            @ put dcache in WT mode
>> +        mcr    p15, 7, r0, c15, c0, 0
>> +#endif
>> +
>>  __armv4_mmu_cache_on:
>>          mov    r12, lr
>>  #ifdef CONFIG_MMU
>> @@ -655,6 +665,12 @@ proc_types:
>>          W(b)    __armv4_mpu_cache_off
>>          W(b)    __armv4_mpu_cache_flush
>>  
>> +        .word    0x41069260        @ ARM926EJ-S (v5TEJ)
>> +        .word    0xff0ffff0
>> +        b    __arm926ejs_mmu_cache_on
>> +        b    __armv4_mmu_cache_off
>> +        b    __armv5tej_mmu_cache_flush
>> +
>>          .word    0x00007000        @ ARM7 IDs
>>          .word    0x0000f000
>>          mov    pc, lr
>> -- 
>> 1.6.2.5.182.ga808d

>    I'd like to know when this will be accepted?
>    DA830/OMAP-L137 are still not bootable in mainline without this 
> patch... :-(

    Russell, I don't see this patch in the patch system. Perhaps, I can add it?

WBR, Sergei