Re: [Intel-gfx] [PATCH v2] drm/i915: Try to sanitize bogus DPLL state left over by broken SNB BIOSen

["Kahola, Mika" <mika.kahola@intel.com>]

The patch look ok to me.

On Fri, 2019-01-11 at 19:49 +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Certain SNB machines (eg. ASUS K53SV) seem to have a broken BIOS
> which misprograms the hardware badly when encountering a suitably
> high resolution display. The programmed pipe timings are somewhat
> bonkers and the DPLL is totally misprogrammed (P divider == 0).
> That will result in atomic commit timeouts as apparently the pipe
> is sufficiently stuck to not signal vblank interrupts.
> 
> IIRC something like this was also observed on some other SNB
> machine years ago (might have been a Dell XPS 8300) but a BIOS
> update cured it. Sadly looks like this was never fixed for the
> ASUS K53SV as the latest BIOS (K53SV.320 11/11/2011) is still
> broken.
> 
> The quickest way to deal with this seems to be to shut down
> the pipe+ports+DPLL. Unfortunately doing this during the
> normal sanitization phase isn't quite soon enough as we
> already spew several WARNs about the bogus hardware state.
> But it's better than hanging the boot for a few dozen seconds.
> Since this is limited to a few old machines it doesn't seem
> entirely worthwile to try and rework the readout+sanitization
> code to handle it more gracefully.
> 
> v2: Fix potential NULL deref (kbuild test robot)
>     Constify has_bogus_dpll_config()
> 
> Cc: stable@vger.kernel.org # v4.20+
> Cc: Daniel Kamil Kozar <dkk089@gmail.com>
> Reported-by: Daniel Kamil Kozar <dkk089@gmail.com>
> Tested-by: Daniel Kamil Kozar <dkk089@gmail.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109245
> Fixes: 516a49cc1946 ("drm/i915: Fix assert_plane() warning on bootup
> with external display")

Reviewed-by: Mika Kahola <mika.kahola@intel.com>

> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 50 ++++++++++++++++++++++++
> ----
>  1 file changed, 44 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c
> b/drivers/gpu/drm/i915/intel_display.c
> index 5dc0de89c49e..6cd6048b4731 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -15438,16 +15438,45 @@ static void intel_sanitize_crtc(struct
> intel_crtc *crtc,
>  	}
>  }
>  
> +static bool has_bogus_dpll_config(const struct intel_crtc_state
> *crtc_state)
> +{
> +	struct drm_i915_private *dev_priv = to_i915(crtc_state-
> >base.crtc->dev);
> +
> +	/*
> +	 * Some SNB BIOSen (eg. ASUS K53SV) are known to misprogram
> +	 * the hardware when a high res displays plugged in. DPLL P
> +	 * divider is zero, and the pipe timings are bonkers. We'll
> +	 * try to disable everything in that case.
> +	 *
> +	 * FIXME would be nice to be able to sanitize this state
> +	 * without several WARNs, but for now let's take the easy
> +	 * road.
> +	 */
> +	return IS_GEN(dev_priv, 6) &&
> +		crtc_state->base.active &&
> +		crtc_state->shared_dpll &&
> +		crtc_state->port_clock == 0;
> +}
> +
>  static void intel_sanitize_encoder(struct intel_encoder *encoder)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
>  	struct intel_connector *connector;
> +	struct intel_crtc *crtc = to_intel_crtc(encoder->base.crtc);
> +	struct intel_crtc_state *crtc_state = crtc ?
> +		to_intel_crtc_state(crtc->base.state) : NULL;
>  
>  	/* We need to check both for a crtc link (meaning that the
>  	 * encoder is active and trying to read from a pipe) and the
>  	 * pipe itself being active. */
> -	bool has_active_crtc = encoder->base.crtc &&
> -		to_intel_crtc(encoder->base.crtc)->active;
> +	bool has_active_crtc = crtc_state &&
> +		crtc_state->base.active;
> +
> +	if (crtc_state && has_bogus_dpll_config(crtc_state)) {
> +		DRM_DEBUG_KMS("BIOS has misprogrammed the hardware.
> Disabling pipe %c\n",
> +			      pipe_name(crtc->pipe));
> +		has_active_crtc = false;
> +	}
>  
>  	connector = intel_encoder_find_connector(encoder);
>  	if (connector && !has_active_crtc) {
> @@ -15458,16 +15487,25 @@ static void intel_sanitize_encoder(struct
> intel_encoder *encoder)
>  		/* Connector is active, but has no active pipe. This is
>  		 * fallout from our resume register restoring. Disable
>  		 * the encoder manually again. */
> -		if (encoder->base.crtc) {
> -			struct drm_crtc_state *crtc_state = encoder-
> >base.crtc->state;
> +		if (crtc_state) {
> +			struct drm_encoder *best_encoder;
>  
>  			DRM_DEBUG_KMS("[ENCODER:%d:%s] manually
> disabled\n",
>  				      encoder->base.base.id,
>  				      encoder->base.name);
> +
> +			/* avoid oopsing in case the hooks consult
> best_encoder */
> +			best_encoder = connector->base.state-
> >best_encoder;
> +			connector->base.state->best_encoder = &encoder-
> >base;
> +
>  			if (encoder->disable)
> -				encoder->disable(encoder,
> to_intel_crtc_state(crtc_state), connector->base.state);
> +				encoder->disable(encoder, crtc_state,
> +						 connector-
> >base.state);
>  			if (encoder->post_disable)
> -				encoder->post_disable(encoder,
> to_intel_crtc_state(crtc_state), connector->base.state);
> +				encoder->post_disable(encoder,
> crtc_state,
> +						      connector-
> >base.state);
> +
> +			connector->base.state->best_encoder =
> best_encoder;
>  		}
>  		encoder->base.crtc = NULL;
>