drm/i915/bios: Extract vbt_signature[]

Replace the three hand rolled "$VBT"s with a vbt_signature[]
to avoid accidents.

v2: Include terminating '\0' for safety (Jani)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923152453.11230-6-ville.syrjala@linux.intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
index 38ea92b4ff13ed8cf3359aa159e5ba4c024d3119..c57426940cf89ff9570d7b03104dd876b3511e71 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_bios.c
+++ b/drivers/gpu/drm/i915/display/intel_bios.c
@@ -2964,6 +2964,9 @@ static const struct bdb_header *get_bdb_header(const struct vbt_header *vbt)
        return _vbt + vbt->bdb_offset;
 }
 
+static const char vbt_signature[] = "$VBT";
+static const int vbt_signature_len = 4;
+
 /**
  * intel_bios_is_valid_vbt - does the given buffer contain a valid VBT
  * @display:   display device
@@ -2986,7 +2989,7 @@ bool intel_bios_is_valid_vbt(struct intel_display *display,
                return false;
        }
 
-       if (memcmp(vbt->signature, "$VBT", 4)) {
+       if (memcmp(vbt->signature, vbt_signature, vbt_signature_len)) {
                drm_dbg_kms(display->drm, "VBT invalid signature\n");
                return false;
        }
@@ -3082,9 +3085,12 @@ 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(vbt_signature_len != sizeof(vbt_signature) - 1);
+       BUILD_BUG_ON(vbt_signature_len != 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 +3150,12 @@ static struct vbt_header *oprom_get_vbt(struct intel_display *display,
        if (!oprom)
                return NULL;
 
+       BUILD_BUG_ON(vbt_signature_len != sizeof(vbt_signature) - 1);
+       BUILD_BUG_ON(vbt_signature_len != 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;