linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915/quirk: Add quirk for devices with incorrect PWM frequency

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Message-ID: <ZU0fa6fvT4ZWTNXr@google.com>
Date:   Thu, 9 Nov 2023 10:05:31 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Allen Ballway <ballway@...omium.org>
Cc:     dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915/quirk: Add quirk for devices with
 incorrect PWM frequency

Hi Allen,

On Tue, Oct 17, 2023 at 06:01:39PM +0000, Allen Ballway wrote:
> Cyernet T10C has a bad default PWM frequency causing the display to
> strobe when the brightness is less than 100%. Create a new quirk to use
> the value from the BIOS rather than the default register value.
> 
> Signed-off-by: Allen Ballway <ballway@...omium.org>
> 
> ---
> 
>  .../gpu/drm/i915/display/intel_backlight.c    |  3 ++-
>  drivers/gpu/drm/i915/display/intel_quirks.c   | 26 +++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_quirks.h   |  1 +
>  3 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c b/drivers/gpu/drm/i915/display/intel_backlight.c
> index 2e8f17c045222..c4dcfece9deca 100644
> --- a/drivers/gpu/drm/i915/display/intel_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_backlight.c
> @@ -1388,7 +1388,8 @@ static int vlv_setup_backlight(struct intel_connector *connector, enum pipe pipe
>  	ctl = intel_de_read(i915, VLV_BLC_PWM_CTL(pipe));
>  	panel->backlight.pwm_level_max = ctl >> 16;
> 
> -	if (!panel->backlight.pwm_level_max)
> +	if (!panel->backlight.pwm_level_max ||
> +	    intel_has_quirk(i915, QUIRK_IGNORE_DEFAULT_PWM_FREQUENCY))
>  		panel->backlight.pwm_level_max = get_backlight_max_vbt(connector);

I think it would be better if we did:

	if (!intel_has_quirk(i915, QUIRK_IGNORE_DEFAULT_PWM_FREQUENCY)) {
		ctl = intel_de_read(i915, VLV_BLC_PWM_CTL(pipe));
		panel->backlight.pwm_level_max = ctl >> 16;
	} else {
		panel->backlight.pwm_level_max = 0;
	}

	if (!panel->backlight.pwm_level_max)
		panel->backlight.pwm_level_max = get_backlight_max_vbt(connector);

The "else" branch can potentially be omitted if we know that backlight
member is initialized to 0 (I suspect it is).

> 
>  	if (!panel->backlight.pwm_level_max)
> diff --git a/drivers/gpu/drm/i915/display/intel_quirks.c b/drivers/gpu/drm/i915/display/intel_quirks.c
> index a280448df771a..ff6cb499428ce 100644
> --- a/drivers/gpu/drm/i915/display/intel_quirks.c
> +++ b/drivers/gpu/drm/i915/display/intel_quirks.c
> @@ -65,6 +65,12 @@ static void quirk_no_pps_backlight_power_hook(struct drm_i915_private *i915)
>  	drm_info(&i915->drm, "Applying no pps backlight power quirk\n");
>  }
> 
> +static void quirk_ignore_default_pwm_frequency(struct drm_i915_private *i915)
> +{
> +	intel_set_quirk(i915, QUIRK_IGNORE_DEFAULT_PWM_FREQUENCY);
> +	drm_info(&i915->drm, "Applying ignore default pwm frequency quirk");
> +}
> +
>  struct intel_quirk {
>  	int device;
>  	int subsystem_vendor;
> @@ -90,6 +96,12 @@ static int intel_dmi_no_pps_backlight(const struct dmi_system_id *id)
>  	return 1;
>  }
> 
> +static int intel_dmi_ignore_default_pwm_frequency(const struct dmi_system_id *id)
> +{
> +	DRM_INFO("Default PWM frequency is incorrect and is overridden on %s\n", id->ident);
> +	return 1;
> +}
> +
>  static const struct intel_dmi_quirk intel_dmi_quirks[] = {
>  	{
>  		.dmi_id_list = &(const struct dmi_system_id[]) {
> @@ -136,6 +148,20 @@ static const struct intel_dmi_quirk intel_dmi_quirks[] = {
>  		},
>  		.hook = quirk_no_pps_backlight_power_hook,
>  	},
> +	{
> +		.dmi_id_list = &(const struct dmi_system_id[]) {
> +			{
> +				.callback = intel_dmi_ignore_default_pwm_frequency,
> +				.ident = "Cybernet T10C Tablet",
> +				.matches = {DMI_EXACT_MATCH(DMI_BOARD_VENDOR,
> +							    "Cybernet Manufacturing Inc."),
> +					    DMI_EXACT_MATCH(DMI_BOARD_NAME, "T10C Tablet"),
> +				},
> +			},
> +			{ }
> +		},
> +		.hook = quirk_ignore_default_pwm_frequency,
> +	},
>  };
> 
>  static struct intel_quirk intel_quirks[] = {
> diff --git a/drivers/gpu/drm/i915/display/intel_quirks.h b/drivers/gpu/drm/i915/display/intel_quirks.h
> index 10a4d163149fd..70589505e5a0e 100644
> --- a/drivers/gpu/drm/i915/display/intel_quirks.h
> +++ b/drivers/gpu/drm/i915/display/intel_quirks.h
> @@ -17,6 +17,7 @@ enum intel_quirk_id {
>  	QUIRK_INVERT_BRIGHTNESS,
>  	QUIRK_LVDS_SSC_DISABLE,
>  	QUIRK_NO_PPS_BACKLIGHT_POWER_HOOK,
> +	QUIRK_IGNORE_DEFAULT_PWM_FREQUENCY

You want a trailing comma here.

>  };
> 
>  void intel_init_quirks(struct drm_i915_private *i915);
> --
> 2.42.0.655.g421f12c284-goog
> 

Thanks.

-- 
Dmitry