Re: [PATCH 2/3] drm/i915: Protect dev_priv->atomic_cdclk_freq with all the crtc locks

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 14-11-16 om 17:35 schreef ville.syrjala@linux.intel.com:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> A modeset on one pipe can update dev_priv->atomic_cdclk_freq without
> actually touching the hardware, in which case we won't force a modeset
> on all the pipes, and thus won't lock any of the other pipes either.
> That means a parallel plane update on another pipe could be looking at
> a stale dev_priv->atomic_cdcdlk_freq and thus fail to notice when the
> plane configuration is invalid, or potentially reject a valid update.
>
> To overcome this we must protect writes to atomic_cdclk_freq with
> all the crtc locks, and thus for reads any single crtc lock will
> be sufficient protection.
>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h      |  9 +++++++-
>  drivers/gpu/drm/i915/intel_display.c | 41 +++++++++++++++++++++++++++++++-----
>  2 files changed, 44 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index c0f1dfc7119e..66d2950dc657 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1874,7 +1874,14 @@ struct drm_i915_private {
>  
>  	unsigned int fsb_freq, mem_freq, is_ddr3;
>  	unsigned int skl_preferred_vco_freq;
> -	unsigned int cdclk_freq, max_cdclk_freq, atomic_cdclk_freq;
> +	unsigned int cdclk_freq, max_cdclk_freq;
> +
> +	/*
> +	 * For reading holding any crtc lock is sufficient,
> +	 * for writing must hold all of them.
> +	 */
> +	unsigned int atomic_cdclk_freq;
> +
>  	unsigned int max_dotclk_freq;
>  	unsigned int rawclk_freq;
>  	unsigned int hpll_freq;
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 70f3f0b70263..d7a4bc63b05b 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -13946,13 +13946,32 @@ static int haswell_mode_set_planes_workaround(struct drm_atomic_state *state)
>  	return 0;
>  }
>  
> +static int intel_lock_all_pipes(struct drm_atomic_state *state)
> +{
> +	struct drm_crtc *crtc;
> +
> +	/* Add all pipes to the state */
> +	for_each_crtc(state->dev, crtc) {
> +		struct drm_crtc_state *crtc_state;
> +
> +		crtc_state = drm_atomic_get_crtc_state(state, crtc);
> +		if (IS_ERR(crtc_state))
> +			return PTR_ERR(crtc_state);
> +	}
> +
> +	return 0;
> +}
> +
>  static int intel_modeset_all_pipes(struct drm_atomic_state *state)
>  {
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *crtc_state;
>  	int ret = 0;
>  
> -	/* add all active pipes to the state */
> +	/*
> +	 * Add all pipes to the state, and force
> +	 * a modeset on all the active ones.
> +	 */
>  	for_each_crtc(state->dev, crtc) {
>  		crtc_state = drm_atomic_get_crtc_state(state, crtc);
>  		if (IS_ERR(crtc_state))
> @@ -14018,12 +14037,24 @@ static int intel_modeset_checks(struct drm_atomic_state *state)
>  		if (ret < 0)
>  			return ret;
>  
> +		/*
> +		 * Writes to dev_priv->atomic_cdclk_freq must protected by
> +		 * holding all the crtc locks, even if we don't end up
> +		 * touching the hardware
> +		 */
> +		if (intel_state->cdclk != dev_priv->atomic_cdclk_freq) {
> +			ret = intel_lock_all_pipes(state);
> +			if (ret < 0)
> +				return ret;
> +		}
> +
Would it be terrible to just use intel_modeset_all_pipes here? Since this can only be different in the all crtc's disabled case
it won't matter much.

~Maarten
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