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

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Message-ID: <1555490771-13242-1-git-send-email-twischer@de.adit-jv.com>
Date:   Wed, 17 Apr 2019 10:46:11 +0200
From:   <twischer@...adit-jv.com>
To:     <patch@...a-project.org>, <broonie@...nel.org>, <perex@...ex.cz>,
        <tiwai@...e.com>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        Timo Wischer <twischer@...adit-jv.com>
Subject: [PATCH] ALSA: pcm: Enable MMAP status and control for ARMv7 and ARMv8

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

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