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 11:40:42 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Timo Wischer <twischer@...adit-jv.com>
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 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@...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?

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@...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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