linux-kernel - [PATCH 1/5] soundwire: bus: add comments to explain interrupt loop filter

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Date:   Tue, 24 Nov 2020 09:33:14 +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,
        gregkh@...uxfoundation.org, jank@...ence.com,
        srinivas.kandagatla@...aro.org, rander.wang@...ux.intel.com,
        ranjani.sridharan@...ux.intel.com, hui.wang@...onical.com,
        pierre-louis.bossart@...ux.intel.com, sanyog.r.kale@...el.com,
        mengdong.lin@...el.com, bard.liao@...el.com
Subject: [PATCH 1/5] soundwire: bus: add comments to explain interrupt loop filter

From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>

The interrupt handling in SoundWire requires software to re-read the
interrupt status after clearing an interrupt. In case the interrupt is
still outstanding, the code in bus.c will loop a number of times,
however that loop is limited to the interrupts detected in the first
read. This strategy helps meet SoundWire requirements without
remaining forever in an interrupt handler.

Add a couple of comments to document this design.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@...ux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@...ux.intel.com>
---
 drivers/soundwire/bus.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index ffe4600fd95b..45131b9f5080 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -1334,6 +1334,7 @@ static int sdw_handle_dp0_interrupt(struct sdw_slave *slave, u8 *slave_status)
 				"SDW_DP0_INT read failed:%d\n", status2);
 			return status2;
 		}
+		/* filter to limit loop to interrupts identified in the first status read */
 		status &= status2;
 
 		count++;
@@ -1404,6 +1405,7 @@ static int sdw_handle_port_interrupt(struct sdw_slave *slave,
 				"SDW_DPN_INT read failed:%d\n", status2);
 			return status2;
 		}
+		/* filter to limit loop to interrupts identified in the first status read */
 		status &= status2;
 
 		count++;
@@ -1589,7 +1591,10 @@ static int sdw_handle_slave_alerts(struct sdw_slave *slave)
 			sdca_cascade = ret & SDW_DP0_SDCA_CASCADE;
 		}
 
-		/* Make sure no interrupts are pending */
+		/*
+		 * Make sure no interrupts are pending, but filter to limit loop
+		 * to interrupts identified in the first status read
+		 */
 		buf &= _buf;
 		buf2[0] &= _buf2[0];
 		buf2[1] &= _buf2[1];
-- 
2.17.1