linux-kernel - [PATCH] drm/msm/dp: Restore aux retry tuning logic

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Message-Id: <20210226210821.682107-1-swboyd@chromium.org>
Date:   Fri, 26 Feb 2021 13:08:21 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Sean Paul <sean@...rly.run>, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org,
        Kuogee Hsieh <khsieh@...eaurora.org>
Subject: [PATCH] drm/msm/dp: Restore aux retry tuning logic

In commit 9fc418430c65 ("drm/msm/dp: unplug interrupt missed after
irq_hpd handler") we dropped a reset of the aux phy during aux transfers
because resetting the phy during active communication caused us to miss
an hpd irq in some cases. Unfortunately, we also dropped the part of the
code that changes the aux phy tuning when an aux transfer fails due to a
timeout. That part of the code was calling into the phy driver to
reconfigure the aux TX swing controls, working around poor channel
quality. Let's restore this phy setting code so that aux channel
communication is more reliable.

Cc: Kuogee Hsieh <khsieh@...eaurora.org>
Fixes: 9fc418430c65 ("drm/msm/dp: unplug interrupt missed after irq_hpd handler")
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---

Noticed by code inspection and based on bug reports where the aux channel
stops working once the commit this is fixing is applied.

 drivers/gpu/drm/msm/dp/dp_aux.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c b/drivers/gpu/drm/msm/dp/dp_aux.c
index 1c6e1d2b947c..7c22bfe0fc7d 100644
--- a/drivers/gpu/drm/msm/dp/dp_aux.c
+++ b/drivers/gpu/drm/msm/dp/dp_aux.c
@@ -32,6 +32,8 @@ struct dp_aux_private {
 	struct drm_dp_aux dp_aux;
 };

+#define MAX_AUX_RETRIES			5
+
 static const char *dp_aux_get_error(u32 aux_error)
 {
 	switch (aux_error) {
@@ -377,6 +379,11 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux *dp_aux,
 	ret = dp_aux_cmd_fifo_tx(aux, msg);

 	if (ret < 0) {
+		if (aux->native) {
+			aux->retry_cnt++;
+			if (!(aux->retry_cnt % MAX_AUX_RETRIES))
+				dp_catalog_aux_update_cfg(aux->catalog);
+		}
 		usleep_range(400, 500); /* at least 400us to next try */
 		goto unlock_exit;
 	}

base-commit: 8b83369ddcb3fb9cab5c1088987ce477565bb630
-- 
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