On Mon, 07 Sep 2026, Arun R Murthy <[email protected]> wrote:
> Its observed that on AUX_CH failure, even if the retry is increased to
> 1000, it does not succeed. Either the command might be wrong or sink in
> an unknown/sleep state can cause this. So try waking the sink device.
> Before reading the DPCD caps wake the sink for eDP.
>
> v2: Use poll_timeout_us (Jani N)
> Add the reason, why this change is required (Ville)
> v3: Wake sink only for eDP
> Remove the dpcd probe set to true/false in wake_sink (Imre)
> v4: make edp_wake_sinc() static and dpcd_readb -> dpcd_reab_byte (Suraj)
>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/4391
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16654
> Signed-off-by: Arun R Murthy <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_dp.c | 34 +++++++++++++++++++++++++
> 1 file changed, 34 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index 0cd5e6b5034c..d4cc5f7e82a4 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -4779,6 +4779,38 @@ intel_edp_set_sink_rates(struct intel_dp *intel_dp)
> intel_edp_set_data_override_rates(intel_dp);
> }
>
> +/* Spec says to try for 3 times, its doubled to add the software overhead */
Where in the spec? What software overhead?
> +#define AUX_CH_WAKE_RETRY 6
There is no guarantee that this is tried 3 or 6 times. The timeout is a
timeout, not retry count.
> +
> +static void intel_edp_wake_sink(struct intel_dp *intel_dp)
> +{
> + u8 value = 0;
> + int ret = 0;
> +
> + /*
> + * Wake the sink device
> + * Spec DP2.1 section 2.3.1.2 if AUX CH is powered down by writing 0x02
> + * to DP_SET_POWER dpcd reg, 1ms time would be required to wake it up
> + */
So this is now talking about 1 ms, but the timeout used is 6 ms.
> + ret = poll_timeout_us(ret = drm_dp_dpcd_read_byte(&intel_dp->aux,
> + DP_SET_POWER, &value),
> + ret == 0, 1000, AUX_CH_WAKE_RETRY * 1000, true);
> +
> + /*
> + * If sink is in D3 then it may not respond to the AUX tx so
> + * wake it up to D3_AUX_ON state
> + * If the above poll_timeout_us fails, try waking the sink.
> + */
> + if (value == DP_SET_POWER_D3 || ret < 0) {
You need to switch the order here. Value may be garbage if ret < 0.
> + /* After setting to D0 need a min of 1ms to wake (Spec DP2.1
> sec 2.3.1.2) */
> + drm_dp_dpcd_write_byte(&intel_dp->aux, DP_SET_POWER,
> + DP_SET_POWER_D0);
> + fsleep(1000);
> + drm_dp_dpcd_write_byte(&intel_dp->aux, DP_SET_POWER,
> + DP_SET_POWER_D3_AUX_ON);
> + }
> +}
> +
> static bool
> intel_edp_init_dpcd(struct intel_dp *intel_dp, struct intel_connector
> *connector)
> {
> @@ -4792,6 +4824,8 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp, struct
> intel_connector *connector
> if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd) != 0)
> return false;
>
> + intel_edp_wake_sink(intel_dp);
> +
> drm_dp_read_desc(&intel_dp->aux, &intel_dp->desc,
> drm_dp_is_branch(intel_dp->dpcd));
> intel_init_dpcd_quirks(intel_dp, &intel_dp->desc.ident);
--
Jani Nikula, Intel
