Re: [PATCH 39/49] drm/i915/chv: use vlv_PLL_is_optimal in chv_find_best_dpll

Jesse Barnes
2015-03-19T20:35:31Z

On 03/17/2015 02:40 AM, Imre Deak wrote:
> Prepare chv_find_best_dpll to be used for BXT too, where we want to
> consider the error between target and calculated frequency too when
> choosing a better PLL configuration.
>
> No functional change.
>
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
> drivers/gpu/drm/i915/intel_display.c | 26 ++++++++++++++++++++------
> 1 file changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 5874512..9ca84a2 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -786,6 +786,16 @@ static bool vlv_PLL_is_optimal(struct drm_device *dev, int target_freq,
> unsigned int best_error_ppm,
> unsigned int *error_ppm)
> {
> + /*
> + * For CHV ignore the error and consider only the P value.
> + * Prefer a bigger P value based on HW requirements.
> + */
> + if (IS_CHERRYVIEW(dev)) {
> + *error_ppm = 0;
> +
> + return calculated_clock->p > best_clock->p;
> + }
> +
> if (WARN_ON_ONCE(!target_freq))
> return false;
>
> @@ -864,11 +874,13 @@ chv_find_best_dpll(const intel_limit_t *limit, struct intel_crtc *crtc,
> intel_clock_t *best_clock)
> {
> struct drm_device *dev = crtc->base.dev;
> + unsigned int best_error_ppm;
> intel_clock_t clock;
> uint64_t m2;
> int found = false;
>
> memset(best_clock, 0, sizeof(*best_clock));
> + best_error_ppm = 1000000;
>
> /*
> * Based on hardware doc, the n always set to 1, and m1 always
> @@ -882,6 +894,7 @@ chv_find_best_dpll(const intel_limit_t *limit, struct intel_crtc *crtc,
> for (clock.p2 = limit->p2.p2_fast;
> clock.p2 >= limit->p2.p2_slow;
> clock.p2 -= clock.p2 > 10 ? 2 : 1) {
> + unsigned int error_ppm;
>
> clock.p = clock.p1 * clock.p2;
>
> @@ -898,12 +911,13 @@ chv_find_best_dpll(const intel_limit_t *limit, struct intel_crtc *crtc,
> if (!intel_PLL_is_valid(dev, limit, &clock))
> continue;
>
> - /* based on hardware requirement, prefer bigger p
> - */
> - if (clock.p > best_clock->p) {
> - *best_clock = clock;
> - found = true;
> - }
> + if (!vlv_PLL_is_optimal(dev, target, &clock, best_clock,
> + best_error_ppm, &error_ppm))
> + continue;
> +
> + *best_clock = clock;
> + best_error_ppm = error_ppm;
> + found = true;
> }
> }
>
>

Looking at it again, maybe vlv_PLL_is_better() might be a better name.

Also, could you just make the ppm variable a scratch one and ignore it?
It just gets set to 0 no matter what, right?

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>