[Intel-gfx] [PATCH] drm/i915: Avoid PPS HW/SW state mismatch due to rounding

[Ville Syrjälä]

On Wed, Nov 29, 2017 at 07:51:37PM +0200, Imre Deak wrote:
> We store a SW state of the t11_t12 timing in 100usec units but have to
> program it in 100msec as required by HW. The rounding used during
> programming means there will be a mismatch between the SW and HW states
> of this value triggering a "PPS state mismatch" error. Avoid this by
> storing the already rounded-up value in the SW state.
> 
> Note that we still calculate panel_power_cycle_delay with the finer
> 100usec granularity to avoid any needless waits using that version of
> the delay.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103903
> Cc: joks <joks at linux.pl>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 957735c0b4c6..27d2529a3416 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -5355,6 +5355,12 @@ intel_dp_init_panel_power_sequencer(struct intel_dp *intel_dp)
>  	 */
>  	final->t8 = 1;
>  	final->t9 = 1;
> +
> +	/*
> +	 * HW has only a 100msec granularity for t11_t12 so round it up
> +	 * accordingly.
> +	 */
> +	final->t11_t12 = roundup(final->t11_t12, 100 * 10);

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

As a micro-optimization I guess we might want to move the division here
as well. But maybe that would cause more confusion since all the other
timings are in 100usec units. Dunno.

>  }
>  
>  static void
> -- 
> 2.13.2
> 
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-- 
Ville Syrjälä
Intel OTC