linux-kernel - Re: [ALSA patch] [PATCH] ALSA: pcm: Enable MMAP status and control for ARMv7 and ARMv8

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Date:   Wed, 17 Apr 2019 11:30:10 +0200
From:   Timo Wischer <twischer@...adit-jv.com>
To:     Takashi Iwai <tiwai@...e.de>
CC:     <broonie@...nel.org>, <perex@...ex.cz>, <tiwai@...e.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [ALSA patch] [PATCH] ALSA: pcm: Enable MMAP status and control
 for ARMv7 and ARMv8

On 4/17/19 11:21, Takashi Iwai wrote:
> On Wed, 17 Apr 2019 10:46:11 +0200,
> <twischer@...adit-jv.com> wrote:
>> From: Timo Wischer <twischer@...adit-jv.com>
>>
>> Since ARMv7 hardware cache coherence is supported.
>> "The SCU maintains coherency between the individual data caches in the
>> Cortex-A5 MPCore processor using a variation of the MOESI protocol" [1].
>>
>> Therefore this patch enables the MMAP access to the status and control
>> structures. This avoids HWSYYNC ioctl calls and therefore lowers the CPU
>> usage.
>>
>> [1] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0434c/
>> BABJECBF.html
> Interesting...  I thought it would never work properly on ARM.
> If it really works like that, I'd happily apply the change.
> But I'd like to hear a confirmation from ARM people before merging
> such an intensive change.

Hi Takashi,

do I need to send this patch to any other mailing list or do you think 
some corresponding guy is already on the lists I have used?

>
>
> thanks,
>
> Takashi
>
>> Signed-off-by: Timo Wischer <twischer@...adit-jv.com>
>> ---
>>   sound/core/pcm_native.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
>> index 1d84529..b8019ef 100644
>> --- a/sound/core/pcm_native.c
>> +++ b/sound/core/pcm_native.c
>> @@ -3225,7 +3225,8 @@ static __poll_t snd_pcm_poll(struct file *file, poll_table *wait)
>>    * Only on coherent architectures, we can mmap the status and the control records
>>    * for effcient data transfer.  On others, we have to use HWSYNC ioctl...
>>    */
>> -#if defined(CONFIG_X86) || defined(CONFIG_PPC) || defined(CONFIG_ALPHA)
>> +#if defined(CONFIG_X86) || defined(CONFIG_PPC) || defined(CONFIG_ALPHA) || \
>> +	(defined(CONFIG_ARM) && defined(CONFIG_CPU_V7)) || defined(CONFIG_ARM64)
>>   /*
>>    * mmap status record
>>    */
>> -- 
>> 2.7.4
>>
>> _______________________________________________
>> Patch mailing list
>> Patch@...a-project.org
>> https://mailman.alsa-project.org/mailman/listinfo/patch
>>

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