[PATCH v3] drm/i915/bdb: Fix version check

[Souza, Jose]

On Thu, 2021-09-30 at 15:46 +0200, Lukasz Majczak wrote:
> With patch "drm/i915/vbt: Fix backlight parsing for VBT 234+"
> the size of bdb_lfp_backlight_data structure has been increased,
> causing if-statement in the parse_lfp_backlight function
> that comapres this structure size to the one retrieved from BDB,
> always to fail for older revisions.
> This patch calculates expected size of the structure for a given
> BDB version and compares it with the value gathered from BDB.
> Tested on Chromebook Pixelbook (Nocturne) (reports bdb->version = 221)

Reviewed-by: José Roberto de Souza <jose.souza at intel.com>

> 
> Tested-by: Lukasz Majczak <lma at semihalf.com>
> Signed-off-by: Lukasz Majczak <lma at semihalf.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c     | 22 ++++++++++++++-----
>  drivers/gpu/drm/i915/display/intel_vbt_defs.h |  5 +++++
>  2 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index 3c25926092de..f9776ca85de3 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -451,13 +451,23 @@ parse_lfp_backlight(struct drm_i915_private *i915,
>  	}
>  
>  	i915->vbt.backlight.type = INTEL_BACKLIGHT_DISPLAY_DDI;
> -	if (bdb->version >= 191 &&
> -	    get_blocksize(backlight_data) >= sizeof(*backlight_data)) {
> -		const struct lfp_backlight_control_method *method;
> +	if (bdb->version >= 191) {
> +		size_t exp_size;
>  
> -		method = &backlight_data->backlight_control[panel_type];
> -		i915->vbt.backlight.type = method->type;
> -		i915->vbt.backlight.controller = method->controller;
> +		if (bdb->version >= 236)
> +			exp_size = sizeof(struct bdb_lfp_backlight_data);
> +		else if (bdb->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];
> +			i915->vbt.backlight.type = method->type;
> +			i915->vbt.backlight.controller = method->controller;
> +		}
>  	}
>  
>  	i915->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 330077c2e588..a2108a8f544d 100644
> --- a/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> +++ b/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> @@ -814,6 +814,11 @@ struct lfp_brightness_level {
>  	u16 reserved;
>  } __packed;
>  
> +#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;
>  	struct lfp_backlight_data_entry data[16];