Re: [PATCH v1] drivers/i915/intel_bios: Fix parsing backlight BDB data

[Ville Syrjälä]

On Tue, Feb 20, 2024 at 02:12:57PM -0700, Karthikeyan Ramasubramanian wrote:
> Starting BDB version 239, hdr_dpcd_refresh_timeout is introduced to
> backlight BDB data. Commit 700034566d68 ("drm/i915/bios: Define more BDB
> contents") updated the backlight BDB data accordingly. This broke the
> parsing of backlight BDB data in VBT for versions 236 - 238 (both
> inclusive) and hence the backlight controls are not responding on units
> with the concerned BDB version.
> 
> backlight_control information has been present in backlight BDB data
> from at least BDB version 191 onwards, if not before. Hence this patch
> extracts the backlight_control information if the block size of
> backlight BDB is >= version 191 backlight BDB block size.
> Tested on Chromebooks using Jasperlake SoC (reports bdb->version = 236).
> Tested on Chromebooks using Raptorlake SoC (reports bdb->version = 251).
> 
> Fixes: 700034566d68 ("drm/i915/bios: Define more BDB contents")
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Signed-off-by: Karthikeyan Ramasubramanian <kramasub@xxxxxxxxxxxx>
> ---
> 
>  drivers/gpu/drm/i915/display/intel_bios.c     | 22 +++++--------------
>  drivers/gpu/drm/i915/display/intel_vbt_defs.h |  2 --
>  2 files changed, 6 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index aa169b0055e97..4ec50903b9e64 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -1041,23 +1041,13 @@ parse_lfp_backlight(struct drm_i915_private *i915,
>  
>  	panel->vbt.backlight.type = INTEL_BACKLIGHT_DISPLAY_DDI;
>  	panel->vbt.backlight.controller = 0;
> -	if (i915->display.vbt.version >= 191) {
> -		size_t exp_size;
> +	if (i915->display.vbt.version >= 191 &&
> +	    get_blocksize(backlight_data) >= EXP_BDB_LFP_BL_DATA_SIZE_REV_191) {

The size checks looks like nonsense to me. I guess maybe
we needed it before we were guaranteed to have the full
struct's worth of memory. But there should be no need for
this anymore.

> +		const struct lfp_backlight_control_method *method;
>  
> -		if (i915->display.vbt.version >= 236)
> -			exp_size = sizeof(struct bdb_lfp_backlight_data);
> -		else if (i915->display.vbt.version >= 234)
> -			exp_size = EXP_BDB_LFP_BL_DATA_SIZE_REV_234;
> -		else
> -			exp_size = EXP_BDB_LFP_BL_DATA_SIZE_REV_191;
> -
> -		if (get_blocksize(backlight_data) >= exp_size) {
> -			const struct lfp_backlight_control_method *method;
> -
> -			method = &backlight_data->backlight_control[panel_type];
> -			panel->vbt.backlight.type = method->type;
> -			panel->vbt.backlight.controller = method->controller;
> -		}
> +		method = &backlight_data->backlight_control[panel_type];
> +		panel->vbt.backlight.type = method->type;
> +		panel->vbt.backlight.controller = method->controller;
>  	}
>  
>  	panel->vbt.backlight.pwm_freq_hz = entry->pwm_freq_hz;
> diff --git a/drivers/gpu/drm/i915/display/intel_vbt_defs.h b/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> index a9f44abfc9fc2..aeea5635a37ff 100644
> --- a/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> +++ b/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> @@ -899,8 +899,6 @@ struct lfp_brightness_level {
>  
>  #define EXP_BDB_LFP_BL_DATA_SIZE_REV_191 \
>  	offsetof(struct bdb_lfp_backlight_data, brightness_level)
> -#define EXP_BDB_LFP_BL_DATA_SIZE_REV_234 \
> -	offsetof(struct bdb_lfp_backlight_data, brightness_precision_bits)
>  
>  struct bdb_lfp_backlight_data {
>  	u8 entry_size;
> -- 
> 2.44.0.rc0.258.g7320e95886-goog

-- 
Ville Syrjälä
Intel