Re: [PATCH v5 3/3] drm/msm/dp: retry 3 times if set sink to D0 poweer state failed

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On 9/12/2022 11:37 AM, Dmitry Baryshkov wrote:
On 12/09/2022 19:23, Kuogee Hsieh wrote:
Bring sink out of D3 (power down) mode into D0 (normal operation) mode
by setting DP_SET_POWER_D0 bit to DP_SET_POWER dpcd register. This
patch will retry 3 times if written to DP_SET_POWER register failed.

Could you please elaborate this change? Can the sink succeed in reading the DP_SET_POWER, but fail writing DP_SET_POWER?

yes, there is possible since it is not only set local sink device but also all downstream sink devices to D0 state.



Changes in v5:
-- split into two patches

Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
---
  drivers/gpu/drm/msm/dp/dp_link.c | 13 ++++++++-----
  1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_link.c b/drivers/gpu/drm/msm/dp/dp_link.c
index 9d5381d..4360728 100644
--- a/drivers/gpu/drm/msm/dp/dp_link.c
+++ b/drivers/gpu/drm/msm/dp/dp_link.c
@@ -50,6 +50,7 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
  {
      u8 value;
      ssize_t len;
+    int i;
        if (link->revision < 0x11)
          return 0;
@@ -61,11 +62,13 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
      value &= ~DP_SET_POWER_MASK;
      value |= DP_SET_POWER_D0;
  -    len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
-    if (len < 0)
-        return len;
-
-    usleep_range(1000, 2000);
+    /* retry for 1ms to give the sink time to wake up */
+    for (i = 0; i < 3; i++) {
+        len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
+        usleep_range(1000, 2000);
+        if (len == 1)
+            break;
+    }
        return 0;
  }




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