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[SRU,OEM-5.10,08/21] UBUNTU: SAUCE: soundwire: bus: add comments to explain interrupt loop filter

Message ID 20201204024132.12905-9-hui.wang@canonical.com
State New
Headers show
Series alsa/sdw: add support for tgl_3_in_1_sdca soundwire machine | expand

Commit Message

Hui Wang Dec. 4, 2020, 2:41 a.m. UTC
From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>

BugLink: https://bugs.launchpad.net/bugs/1906738

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@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
(cherry picked from commit 961b0d814ddd27d0e5840c5bcac15088d6b00f72
git://github.com/thesofproject/linux.git topic/sof-dev-rebase)
Signed-off-by: Hui Wang <hui.wang@canonical.com>
---
 drivers/soundwire/bus.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
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Patch

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];