linux-kernel - Re: [PATCH] drm/amd/display: add parameter backlight

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Date:   Mon, 31 Oct 2022 10:24:25 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     Filip Moc <dev@...6.cz>, Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: add parameter backlight_min

On 2022-10-29 15:13, Filip Moc wrote:
> There are some devices on which amdgpu won't allow user to set brightness
> to sufficiently low values even though the hardware would support it just
> fine.
> 
> This usually happens in two cases when either configuration of brightness
> levels via ACPI/ATIF is not available and amdgpu falls back to defaults
> (currently 12 for minimum level) which may be too high for some devices or
> even the configuration via ATIF is available but the minimum brightness
> level provided by the manufacturer is set to unreasonably high value.
> 
> In either case user can use this new module parameter to adjust the
> minimum allowed backlight brightness level.
> 

Thanks for this patch and covering all the bases.

It might be useful to have an example in the commit description on
how to set the array property. I assume it looks like this if I
wanted to set the first device to a minimum of 2 and leave the default
for the 2nd one:

amdgpu.backlight_min=2:-1

Either way, this patch is
Reviewed-by: Harry Wentland <harry.wentland@....com>

Harry

> Link: https://bugzilla.kernel.org/show_bug.cgi?id=203439>> 
> Signed-off-by: Filip Moc <dev@...6.cz>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu.h               |  3 +++
>  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c           | 15 +++++++++++++++
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 15 +++++++++++++++
>  3 files changed, 33 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> index 0e6ddf05c23c..c5445402c49d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> @@ -200,6 +200,9 @@ extern uint amdgpu_dc_debug_mask;
>  extern uint amdgpu_dc_visual_confirm;
>  extern uint amdgpu_dm_abm_level;
>  extern int amdgpu_backlight;
> +#ifdef CONFIG_DRM_AMD_DC
> +extern int amdgpu_backlight_override_min[];
> +#endif
>  extern struct amdgpu_mgpu_info mgpu_info;
>  extern int amdgpu_ras_enable;
>  extern uint amdgpu_ras_mask;
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> index 16f6a313335e..f2fb549ac52f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> @@ -43,6 +43,7 @@
>  #include "amdgpu_irq.h"
>  #include "amdgpu_dma_buf.h"
>  #include "amdgpu_sched.h"
> +#include "amdgpu_dm.h"
>  #include "amdgpu_fdinfo.h"
>  #include "amdgpu_amdkfd.h"
>  
> @@ -853,6 +854,20 @@ int amdgpu_backlight = -1;
>  MODULE_PARM_DESC(backlight, "Backlight control (0 = pwm, 1 = aux, -1 auto (default))");
>  module_param_named(backlight, amdgpu_backlight, bint, 0444);
>  
> +/**
> + * DOC: backlight_min (array of int)
> + * Override minimum allowed backlight brightness signal (per display).
> + * Must be less than the maximum brightness signal.
> + * Negative value means no override.
> + *
> + * Defaults to all -1 (no override on any display).
> + */
> +#ifdef CONFIG_DRM_AMD_DC
> +int amdgpu_backlight_override_min[AMDGPU_DM_MAX_NUM_EDP] = {[0 ... (AMDGPU_DM_MAX_NUM_EDP-1)] = -1};
> +MODULE_PARM_DESC(backlight_min, "Override minimum backlight brightness signal (0..max-1, -1 = no override (default))");
> +module_param_array_named(backlight_min, amdgpu_backlight_override_min, int, NULL, 0444);
> +#endif
> +
>  /**
>   * DOC: tmz (int)
>   * Trusted Memory Zone (TMZ) is a method to protect data being written
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index eb4ce7216104..e2c36ba93d05 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -3911,6 +3911,21 @@ static void amdgpu_dm_update_backlight_caps(struct amdgpu_display_manager *dm,
>  	dm->backlight_caps[bl_idx].min_input_signal = AMDGPU_DM_DEFAULT_MIN_BACKLIGHT;
>  	dm->backlight_caps[bl_idx].max_input_signal = AMDGPU_DM_DEFAULT_MAX_BACKLIGHT;
>  #endif
> +
> +	if (amdgpu_backlight_override_min[bl_idx] >= 0) {
> +		if (amdgpu_backlight_override_min[bl_idx] < dm->backlight_caps[bl_idx].max_input_signal) {
> +			DRM_INFO("amdgpu: backlight[%i]: overriding minimum brightness from %i to %i\n",
> +				  bl_idx,
> +				  dm->backlight_caps[bl_idx].min_input_signal,
> +				  amdgpu_backlight_override_min[bl_idx]);
> +			dm->backlight_caps[bl_idx].min_input_signal = amdgpu_backlight_override_min[bl_idx];
> +		} else {
> +			DRM_ERROR("amdgpu: backlight[%i]: minimum brightness override (%i) is not below maximum (%i)\n",
> +				  bl_idx,
> +				  amdgpu_backlight_override_min[bl_idx],
> +				  dm->backlight_caps[bl_idx].max_input_signal);
> +		}
> +	}
>  }
>  
>  static int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps,
> 
> base-commit: d8c03bfe146fd5e081a252cd34f3f12ca0255357