[PATCH 4/5] drm/i915/bios: Extract vbt_signature[]

[Jani Nikula]

On Tue, 10 Sep 2024, Ville Syrjala <ville.syrjala at linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> Replace the three hand rolled "$VBT"s with a vbt_signature[]
> to avoid accidents.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index cbbda94c3dab..0b92b494117f 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -2964,6 +2964,8 @@ static const struct bdb_header *get_bdb_header(const struct vbt_header *vbt)
>  	return _vbt + vbt->bdb_offset;
>  }
>  
> +static const char vbt_signature[4] = "$VBT";

Always a bit scary to add strings without termination, but I guess it's
justified here.

Reviewed-by: Jani Nikula <jani.nikula at intel.com>


> +
>  /**
>   * intel_bios_is_valid_vbt - does the given buffer contain a valid VBT
>   * @display:	display device
> @@ -2986,7 +2988,7 @@ bool intel_bios_is_valid_vbt(struct intel_display *display,
>  		return false;
>  	}
>  
> -	if (memcmp(vbt->signature, "$VBT", 4)) {
> +	if (memcmp(vbt->signature, vbt_signature, sizeof(vbt_signature))) {
>  		drm_dbg_kms(display->drm, "VBT invalid signature\n");
>  		return false;
>  	}
> @@ -3082,9 +3084,11 @@ static struct vbt_header *spi_oprom_get_vbt(struct intel_display *display,
>  	oprom_offset = intel_uncore_read(&i915->uncore, OROM_OFFSET);
>  	oprom_offset &= OROM_OFFSET_MASK;
>  
> +	BUILD_BUG_ON(sizeof(vbt_signature) != sizeof(u32));
> +
>  	for (count = 0; count < oprom_size; count += 4) {
>  		data = intel_spi_read32(&i915->uncore, oprom_offset + count);
> -		if (data == *((const u32 *)"$VBT")) {
> +		if (data == *((const u32 *)vbt_signature)) {
>  			found = oprom_offset + count;
>  			break;
>  		}
> @@ -3144,9 +3148,11 @@ static struct vbt_header *oprom_get_vbt(struct intel_display *display,
>  	if (!oprom)
>  		return NULL;
>  
> +	BUILD_BUG_ON(sizeof(vbt_signature) != sizeof(u32));
> +
>  	/* Scour memory looking for the VBT signature. */
>  	for (i = 0; i + 4 < size; i += 4) {
> -		if (ioread32(oprom + i) != *((const u32 *)"$VBT"))
> +		if (ioread32(oprom + i) != *((const u32 *)vbt_signature))
>  			continue;
>  
>  		p = oprom + i;

-- 
Jani Nikula, Intel