[Intel-gfx] [PATCH 3/3] drm/i915: Bump CHV PFI credits to 63 when cdclk>=czclk
Clint Taylor
clinton.a.taylor at intel.com
Fri Jun 12 09:24:24 PDT 2015
On 05/26/2015 10:22 AM, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> Switch from using 31 PFI credits to 63 PFI credits when cdclk>=czclk on
> CHV. The spec lists both 31 and 63 as "suggested" values, but based on
> feedback from hardware folks we should actually be using 63. Originally
> I picked the 31 basically by flipping a coin.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
> drivers/gpu/drm/i915/intel_display.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 067b1de..44b9c54 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -5986,7 +5986,7 @@ static void vlv_program_pfi_credits(struct drm_i915_private *dev_priv)
> if (DIV_ROUND_CLOSEST(dev_priv->cdclk_freq, 1000) >= dev_priv->rps.cz_freq) {
> /* CHV suggested value is 31 or 63 */
> if (IS_CHERRYVIEW(dev_priv))
> - credits = PFI_CREDIT_31;
> + credits = PFI_CREDIT_63;
> else
> credits = PFI_CREDIT(15);
> } else {
>
Although not part of this review the else clause is setting PFI_CREDIT
to 15 when the BPSEC states that the default of 8 should be used when
cdclk/czclk < 1. According to the original patch, 15 is the optimal
value as stated by another driver team.
Reviewed-by: Clint Taylor <Clinton.A.Taylor at intel.com>
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