2021-02-08 23:46:02

by Lyude Paul

Subject: [RFC v4 08/11] drm/i915/dpcd_bl: Return early in vesa_calc_max_backlight if we can't read PWMGEN_BIT_COUNT

If we can't read DP_EDP_PWMGEN_BIT_COUNT in
intel_dp_aux_vesa_calc_max_backlight() but do have a valid PWM frequency
defined in the VBT, we'll keep going in the function until we inevitably
fail on reading DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN. There's not much point in
doing this, so just return early.

Signed-off-by: Lyude Paul <[email protected]>
---
drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 611eb3a7cc08..a139f0e08839 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -449,11 +449,14 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
u8 pn, pn_min, pn_max;

- if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) == 1) {
- pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
- max_backlight = (1 << pn) - 1;
+ if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) != 1) {
+ drm_dbg_kms(&i915->drm, "Failed to read pwmgen bit count cap\n");
+ return 0;
}

+ pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+ max_backlight = (1 << pn) - 1;
+
/* Find desired value of (F x P)
* Note that, if F x P is out of supported range, the maximum value or
* minimum value will applied automatically. So no need to check that.
--
2.29.2

2021-02-11 04:00:23

by Rodrigo Vivi

Subject: Re: [Intel-gfx] [RFC v4 08/11] drm/i915/dpcd_bl: Return early in vesa_calc_max_backlight if we can't read PWMGEN_BIT_COUNT

On Mon, Feb 08, 2021 at 06:38:58PM -0500, Lyude Paul wrote:
> If we can't read DP_EDP_PWMGEN_BIT_COUNT in
> intel_dp_aux_vesa_calc_max_backlight() but do have a valid PWM frequency
> defined in the VBT, we'll keep going in the function until we inevitably
> fail on reading DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN. There's not much point in
> doing this, so just return early.
>
> Signed-off-by: Lyude Paul <[email protected]>

Reviewed-by: Rodrigo Vivi <[email protected]>

> ---
> drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> index 611eb3a7cc08..a139f0e08839 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -449,11 +449,14 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
> int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> u8 pn, pn_min, pn_max;
>
> - if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) == 1) {
> - pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> - max_backlight = (1 << pn) - 1;
> + if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) != 1) {
> + drm_dbg_kms(&i915->drm, "Failed to read pwmgen bit count cap\n");
> + return 0;
> }
>
> + pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> + max_backlight = (1 << pn) - 1;
> +
> /* Find desired value of (F x P)
> * Note that, if F x P is out of supported range, the maximum value or
> * minimum value will applied automatically. So no need to check that.
> --
> 2.29.2
>
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