On Wed, Aug 23, 2017 at 06:12:51PM +0530, Shashank Sharma wrote:
> From the CI builds, its been observed that during a driver
> reload/insert, dp dual mode read function sometimes fails to
> read from dual mode devices (like LSPCON) over i2c-over-aux
> channel.
>
> This patch:
> - adds some delay and few retries, allowing a scope for these
> devices to settle down and respond.
> - changes one error log's level from ERROR->DEBUG as we want
> to call it an error only after all the retries are exhausted.
>
> V2: Addressed review comments from Jani (for loop for retry)
>
> Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Imre Deak <imre.deak@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxxxx>
> ---
> drivers/gpu/drm/drm_dp_dual_mode_helper.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> index 80e62f6..09bf962 100644
> --- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> +++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> @@ -75,8 +75,16 @@ ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> },
> };
> int ret;
> + int retry;
> +
> + for (retry = 0; retry < 6; retry++) {
> + if (retry)
> + usleep_range(500, 1000);
> + ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
> + if (ret > 0)
I think the ret == 0 case should be handled with the rest of
partial-read cases (which we check against further down). So the above
should be
if (ret >= 0)
With this fixed it looks ok to me, so fwiw:
Reviewed-by: Imre Deak <imre.deak@xxxxxxxxx>
Note that ideally we wouldn't retry for error returns like
-ENOTSUPPORTED, -ENOMEM, -E2BIG, but it's not a big deal to do that
either. One possibility to solving that and also making this workaround
more generic is to reuse the existing retry logic in __i2c_transfer() by
making it retry in all relevant error cases (timeout/IO) and setting
i2c_adapter::retries for the LSPCON adaptor. But that can be done as a
follow-up.
> + break;
> + }
>
> - ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
> if (ret < 0)
> return ret;
> if (ret != ARRAY_SIZE(msgs))
> @@ -420,7 +428,7 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
> ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_LSPCON_CURRENT_MODE,
> &data, sizeof(data));
> if (ret < 0) {
> - DRM_ERROR("LSPCON read(0x80, 0x41) failed\n");
> + DRM_DEBUG_KMS("LSPCON read(0x80, 0x41) failed\n");
> return -EFAULT;
> }
>
> --
> 2.7.4
>
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