Re: [PATCH v3] drm/i915/dp: Do not reset detect_done flag in intel_dp_detect

[Manasi Navare <manasi.d.navare@intel.com>]

I have verified this patch with the latest drm-tip and it is also
absolutely necessary to ensure the link gets properly retrained
after link-status is BAD and after anew modeset is triggered by
userspace. Without this patch, since intel_dp_long_pulse gets called
it resets the link failure values and link retraining does not happen
at lower link rates.

Ville/Jani could you please review this patch?
Thi is definitely a bug in the existing codebase and we need to get this merged
soon to get it fixed.

Regards
Manasi

On Thu, Dec 29, 2016 at 11:14:28PM -0800, Dhinakaran Pandiyan wrote:
> From: "Navare, Manasi D" <manasi.d.navare@intel.com>
> 
> The detect_done flag was introduced in the 'commit 7d23e3c37bb3
> ("drm/i915: Cleaning up intel_dp_hpd_pulse")' in order to avoid multiple
> detects on hotplug where intel_dp_long_pulse() was called from HPD handler
> as well as intel_dp_detect(). Later, 'commit 1015811609c0
> ("drm/i915: Move long hpd handling into the hotplug work")' deferred long
> hpd handling to hotplug work to avoid handling it twice. But, resetting the
> flag after long hpd handling leads to the code being executed again during
> mode enumeration.
> 
> So, do not reset the detect_done flag to False in intel_dp_detect(). The
> flag is reset in intel_dp_hpd_pulse() to allow a full detect and set when
> the hotplug work does a full DPCD detect. However if ->detect() gets called
> during mode enumeration after a DPCD detect, return the cached connector
> status.
> 
> Resetting the flag in the encoder's reset callback should take care of
> hotplug between suspend/resume.
> 
> v2:
> Allow full detect after encoder reset. (Ville)
> Set the detect_done flag for connector disconnected case too. (DK)
> Commit message changes.
> 
> Cc: stable@vger.kernel.org
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Ander Conselvande Oliveira <ander.conselvan.de.oliveira@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Fixes: commit 7d23e3c37bb3 ("drm/i915: Cleaning up intel_dp_hpd_pulse")
> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index fb12896..6732c17 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4516,7 +4516,6 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
>  	intel_dp_set_edid(intel_dp);
>  	if (is_edp(intel_dp) || intel_connector->detect_edid)
>  		status = connector_status_connected;
> -	intel_dp->detect_done = true;
>  
>  	/* Try to read the source of the interrupt */
>  	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11 &&
> @@ -4551,10 +4550,10 @@ intel_dp_detect(struct drm_connector *connector, bool force)
>  		      connector->base.id, connector->name);
>  
>  	/* If full detect is not performed yet, do a full detect */
> -	if (!intel_dp->detect_done)
> +	if (!intel_dp->detect_done) {
> +		intel_dp->detect_done = true;
>  		status = intel_dp_long_pulse(intel_dp->attached_connector);
> -
> -	intel_dp->detect_done = false;
> +	}
>  
>  	return status;
>  }
> @@ -4859,6 +4858,8 @@ void intel_dp_encoder_reset(struct drm_encoder *encoder)
>  	if (lspcon->active)
>  		lspcon_resume(lspcon);
>  
> +	intel_dp->detect_done = false;
> +
>  	pps_lock(intel_dp);
>  
>  	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
> -- 
> 2.7.4
>