[PATCH] drm/i915/psr: WA for panels stating bad link status after PSR is enabled

[Jani Nikula]

On Mon, 28 Oct 2024, Jouni Högander <jouni.hogander at intel.com> wrote:
> We are currently seeing unexpected link trainings with several different
> eDP panels. These are caused by these panels stating bad link status in
> their dpcd registers. This can be observed by doing following test:
>
> 1. Boot up without Xe module loaded
>
> 2. Load Xe module with PSR disabled:
>     $ modprobe xe  enable_psr=0
>
> 3. Read panel link status register
>     $ dpcd_reg read --offset 0x200e --count=1
>     0x200e:  00
>
> 4. Enable PSR, sleep for 2 seconds and disable PSR again:
>
>     $ echo 0x1 > /sys/kernel/debug/dri/0/i915_edp_psr_debug
>     $ echo "-1" > /sys/kernel/debug/dri/0000:00:02.0/xe_params/enable_psr
>     $ echo 0x0 > /sys/kernel/debug/dri/0/i915_edp_psr_debug
>     $ sleep 2
>     $ cat /sys/kernel/debug/dri/0/i915_edp_psr_status | grep status
>     $ echo 0x1 > /sys/kernel/debug/dri/0/i915_edp_psr_debug
>     Source PSR/PanelReplay status: DEEP_SLEEP [0x80310030]
>
> 5. Now read panel link status registers again:
>     $ dpcd_reg read --offset 0x200e --count=1
>     0x200e:  80
>
> Workaround this by not trusting link status registers after PSR is enabled
> until first short pulse interrupt is received.

Which eDP/DPCD version are we talking about?

Could this be related to AUX-less ALPM?

Some nitpicks below, less important.

> Signed-off-by: Jouni Högander <jouni.hogander at intel.com>
> ---
>  .../drm/i915/display/intel_display_types.h    |  2 +
>  drivers/gpu/drm/i915/display/intel_dp.c       |  3 +-
>  drivers/gpu/drm/i915/display/intel_psr.c      | 39 +++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_psr.h      |  1 +
>  4 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 2bb1fa64da2f..f0b7d7262961 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1618,6 +1618,8 @@ struct intel_psr {
>  	u32 dc3co_exit_delay;
>  	struct delayed_work dc3co_work;
>  	u8 entry_setup_frames;
> +
> +	bool link_ok;
>  };
>  
>  struct intel_dp {
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index b036c6521659..efaaadfb12ea 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5007,7 +5007,8 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
>  		return true;
>  
>  	/* Retrain if link not ok */
> -	return !intel_dp_link_ok(intel_dp, link_status);
> +	return !(intel_dp_link_ok(intel_dp, link_status) ||
> +		 intel_psr_link_ok(intel_dp));

Nitpick, in general I think "not A and not B" reads better than "not (A
or B)" because saying the parens aloud is kind of clumsy. Reading code
aloud (well, in my head anyway) is one of my main tests for readability.

>  }
>  
>  bool intel_dp_has_connector(struct intel_dp *intel_dp,
> diff --git a/drivers/gpu/drm/i915/display/intel_psr.c b/drivers/gpu/drm/i915/display/intel_psr.c
> index 992543f508c1..0cd7388389e0 100644
> --- a/drivers/gpu/drm/i915/display/intel_psr.c
> +++ b/drivers/gpu/drm/i915/display/intel_psr.c
> @@ -2009,6 +2009,15 @@ static void intel_psr_enable_locked(struct intel_dp *intel_dp,
>  	intel_dp->psr.enabled = true;
>  	intel_dp->psr.paused = false;
>  
> +	/*
> +	 * Link_ok is sticky and set here on PSR enable. We can assume link
> +	 * training is complete as we never continue to PSR enable with
> +	 * untrained link. Link_ok is kept as set until first short pulse
> +	 * interrupt. This is targeted to workaround panels stating bad link
> +	 * after PSR is enabled.
> +	 */
> +	intel_dp->psr.link_ok = true;
> +
>  	intel_psr_activate(intel_dp);
>  }
>  
> @@ -3458,6 +3467,9 @@ void intel_psr_short_pulse(struct intel_dp *intel_dp)
>  
>  	mutex_lock(&psr->lock);
>  
> +	/* Let's clear possibly set link_ok flag here */

That's kind of a translation of C into English. If you need the comment,
then maybe state the why instead of the what?

> +	psr->link_ok = false;
> +
>  	if (!psr->enabled)
>  		goto exit;
>  
> @@ -3517,6 +3529,33 @@ bool intel_psr_enabled(struct intel_dp *intel_dp)
>  	return ret;
>  }
>  
> +/**
> + * intel_psr_link_ok - return psr->link_ok
> + * @intel_dp: struct intel_dp
> + *
> + * We are seeing unexpected link re-trainings with some panels. This is caused
> + * by panel stating bad link status after PSR is enabled. Code checking link
> + * status can call this to ensure it can ignore bad link status stated by the
> + * panel I.e. if panel is stating bad link and intel_psr_link_ok is stating link
> + * is ok caller should rely on latter.
> + *
> + * Return value of link_ok
> + */
> +bool intel_psr_link_ok(struct intel_dp *intel_dp)
> +{
> +	bool ret;
> +
> +	if ((!CAN_PSR(intel_dp) && !CAN_PANEL_REPLAY(intel_dp)) ||
> +	    !intel_dp_is_edp(intel_dp))
> +		return false;
> +
> +	mutex_lock(&intel_dp->psr.lock);
> +	ret = intel_dp->psr.link_ok;
> +	mutex_unlock(&intel_dp->psr.lock);
> +
> +	return ret;
> +}
> +
>  /**
>   * intel_psr_lock - grab PSR lock
>   * @crtc_state: the crtc state
> diff --git a/drivers/gpu/drm/i915/display/intel_psr.h b/drivers/gpu/drm/i915/display/intel_psr.h
> index 5f26f61f82aa..956be263c09e 100644
> --- a/drivers/gpu/drm/i915/display/intel_psr.h
> +++ b/drivers/gpu/drm/i915/display/intel_psr.h
> @@ -59,6 +59,7 @@ void intel_psr2_program_trans_man_trk_ctl(const struct intel_crtc_state *crtc_st
>  void intel_psr_pause(struct intel_dp *intel_dp);
>  void intel_psr_resume(struct intel_dp *intel_dp);
>  bool intel_psr_needs_block_dc_vblank(const struct intel_crtc_state *crtc_state);
> +bool intel_psr_link_ok(struct intel_dp *intel_dp);
>  
>  void intel_psr_lock(const struct intel_crtc_state *crtc_state);
>  void intel_psr_unlock(const struct intel_crtc_state *crtc_state);

-- 
Jani Nikula, Intel