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Date:   Wed, 17 Apr 2019 11:21:48 +0200
Message-ID: <s5hlg093s2b.wl-tiwai@suse.de>
From:   Takashi Iwai <tiwai@suse.de>
To:     <twischer@de.adit-jv.com>
Cc:     <broonie@kernel.org>, <perex@perex.cz>, <tiwai@suse.com>,
        alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
Subject: Re: [ALSA patch] [PATCH] ALSA: pcm: Enable MMAP status and control for ARMv7 and ARMv8
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On Wed, 17 Apr 2019 10:46:11 +0200,
<twischer@de.adit-jv.com> wrote:
> 
> From: Timo Wischer <twischer@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.


thanks,

Takashi

> 
> Signed-off-by: Timo Wischer <twischer@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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