[alsa-devel] [ALSA patch] [PATCH] ALSA: pcm: Enable MMAP status and control for ARMv7 and ARMv8

[Timo Wischer]

Hello all,

it would be great if someone from Renesas or someone else could 
acknowledge the patch.
I think it is a good improvement especially when using ALSA plugins like 
dmix.

Feel free to forward if you know someone who is aware of the cache 
coherency of ARM architectures.

Best regards
*Timo Wischer*
Engineering Software Multimedia (ADITG/ESM)

Tel. +49 5121 49 6938
On 4/17/19 11:40 AM, Takashi Iwai wrote:
> On Wed, 17 Apr 2019 11:30:10 +0200,
> Timo Wischer wrote:
>> On 4/17/19 11:21, Takashi Iwai wrote:
>>> On Wed, 17 Apr 2019 10:46:11 +0200,
>>> <twischer at de.adit-jv.com> wrote:
>>>> From: Timo Wischer <twischer at de.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?
> Well, maybe we need to ping ARM people if no one on the lists you
> Cc'ed give comments.  Let's see.
>
>
> Takashi
>
>>>
>>> thanks,
>>>
>>> Takashi
>>>
>>>> Signed-off-by: Timo Wischer <twischer at de.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
>>>>
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>>>>