[Intel-gfx] [PATCH v1] drm/i915/bdb: Fix version check

[Souza, Jose]

On Mon, 2021-09-20 at 16:11 +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 fixes it by comparing a total size of all fileds from
> the structure (present before the change) with the value gathered from BDB.
> Tested on Chromebook Pixelbook (Nocturne) (reports bdb->version = 221)
> 
> Cc: <stable at vger.kernel.org> # 5.4+
> 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     | 4 +++-
>  drivers/gpu/drm/i915/display/intel_vbt_defs.h | 5 +++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index 3c25926092de..052a19b455d1 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -452,7 +452,9 @@ 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)) {
> +	    get_blocksize(backlight_data) >= (sizeof(backlight_data->entry_size) +
> +					      sizeof(backlight_data->data) +
> +					      sizeof(backlight_data->level))) {

Missing sizeof(backlight_data->backlight_control) but this is getting very verbose.
Would be better have a expected size variable set each version set in the beginning of this function.

something like:
switch (bdb->version) {
case 191:
	expected_size = x;
	break;
case 234:
	expected_size = x;
	break;
case 236:
default:
	expected_size = x;
}
	

>  		const struct lfp_backlight_control_method *method;
>  
>  		method = &backlight_data->backlight_control[panel_type];
> diff --git a/drivers/gpu/drm/i915/display/intel_vbt_defs.h b/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> index 330077c2e588..fff456bf8783 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;
>  
> +/*
> + * Changing struct bdb_lfp_backlight_data might affect its
> + * size comparation to the value hold in BDB.
> + * (e.g. in parse_lfp_backlight())
> + */

This is true for all the blocks so I don't think we need this comment.

>  struct bdb_lfp_backlight_data {
>  	u8 entry_size;
>  	struct lfp_backlight_data_entry data[16];