Re: [PATCH 1/4] msm: scm: Mark inline asm as volatile

[Stephen Boyd <sboyd@codeaurora.org>]

On 02/25/2011 03:56 AM, Will Deacon wrote:
> Hi Stephen,
>
> On Thu, 2011-02-24 at 18:44 +0000, Stephen Boyd wrote:
>> We don't want the compiler to remove these asm statements or
>> reorder them in any way. Mark them as volatile to be sure.
>>
>> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
>> ---
>>  arch/arm/mach-msm/scm.c |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/mach-msm/scm.c b/arch/arm/mach-msm/scm.c
>> index f4b9bc9..ba57b5a 100644
>> --- a/arch/arm/mach-msm/scm.c
>> +++ b/arch/arm/mach-msm/scm.c
>> @@ -174,7 +174,7 @@ static u32 smc(u32 cmd_addr)
>>         register u32 r0 asm("r0") = 1;
>>         register u32 r1 asm("r1") = (u32)&context_id;
>>         register u32 r2 asm("r2") = cmd_addr;
>> -       asm(
>> +       asm volatile(
>>                 __asmeq("%0", "r0")
>>                 __asmeq("%1", "r0")
>>                 __asmeq("%2", "r1")
>> @@ -271,7 +271,7 @@ u32 scm_get_version(void)
>>                 return version;
>>
>>         mutex_lock(&scm_lock);
>> -       asm(
>> +       asm volatile(
>>                 __asmeq("%0", "r1")
>>                 __asmeq("%1", "r0")
>>                 __asmeq("%2", "r1")
>
>
> These asm blocks all have sensible looking output constraints. Why
> do they need to be marked volatile?

I'm not seeing any different code with or without this so I saw little
harm in marking them as volatile. I really don't want the compiler
moving them or deleting them so it seemed safer to just mark it volatile
to make sure nothing happens to the smc instructions.

-- 
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The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.