linux-kernel - [PATCH] soundwire: intel: read AC timing control register before updating it

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Message-Id: <20230515081301.12921-1-yung-chuan.liao@linux.intel.com>
Date:   Mon, 15 May 2023 16:13:01 +0800
From:   Bard Liao <yung-chuan.liao@...ux.intel.com>
To:     alsa-devel@...a-project.org, vkoul@...nel.org
Cc:     vinod.koul@...aro.org, linux-kernel@...r.kernel.org,
        pierre-louis.bossart@...ux.intel.com, bard.liao@...el.com
Subject: [PATCH] soundwire: intel: read AC timing control register before updating it

From: Chao Song <chao.song@...ux.intel.com>

Start from ACE1.x, DOAISE is added to AC timing control
register bit 5, it combines with DOAIS to get effective
timing, and has the default value 1.

The current code fills DOAIS, DACTQE and DODS bits to a
variable initialized to zero, and updates the variable
to AC timing control register. With this operation, We
change DOAISE to 0, and force a much more aggressive
timing. The timing is even unable to form a working
waveform on SDA pin on Meteorlake.

This patch uses read-modify-write operation for the AC
timing control register access, thus makes sure those
bits not supposed and intended to change are not touched.

Signed-off-by: Chao Song <chao.song@...ux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Reviewed-by: Rander Wang <rander.wang@...el.com>
Signed-off-by: Bard Liao <yung-chuan.liao@...ux.intel.com>
---
 drivers/soundwire/intel.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/intel.c b/drivers/soundwire/intel.c
index 238acf5c97a9..8cd2c73ac66f 100644
--- a/drivers/soundwire/intel.c
+++ b/drivers/soundwire/intel.c
@@ -260,7 +260,7 @@ static void intel_shim_init(struct sdw_intel *sdw)
 {
 	void __iomem *shim = sdw->link_res->shim;
 	unsigned int link_id = sdw->instance;
-	u16 ioctl = 0, act = 0;
+	u16 ioctl = 0, act;
 
 	/* Initialize Shim */
 	ioctl |= SDW_SHIM_IOCTL_BKE;
@@ -281,6 +281,7 @@ static void intel_shim_init(struct sdw_intel *sdw)
 
 	intel_shim_glue_to_master_ip(sdw);
 
+	act = intel_readw(shim, SDW_SHIM_CTMCTL(link_id));
 	u16p_replace_bits(&act, 0x1, SDW_SHIM_CTMCTL_DOAIS);
 	act |= SDW_SHIM_CTMCTL_DACTQE;
 	act |= SDW_SHIM_CTMCTL_DODS;
-- 
2.25.1