[Intel-gfx] [PATCH 3/3] drm/i915/i915: assume vbt is 4-byte aligned into oprom

[Lucas De Marchi]

The unaligned ioread32() will make us read byte by byte looking for the
vbt. We could just as well have done a ioread8() + a shift and avoid the
extra confusion on how we are looking for "$VBT".

However when using ACPI it's guaranteed the VBT is 4-byte aligned
per spec, so we can probably assume it here as well.

Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
---
 drivers/gpu/drm/i915/display/intel_bios.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
index 3ab73f8db8dd..328bc6b6157f 100644
--- a/drivers/gpu/drm/i915/display/intel_bios.c
+++ b/drivers/gpu/drm/i915/display/intel_bios.c
@@ -1802,27 +1802,20 @@ static struct vbt_header *oprom_get_vbt(struct drm_i915_private *dev_priv)
 	void __iomem *p = NULL, __iomem *oprom;
 	struct vbt_header *vbt;
 	u16 vbt_size;
-	size_t i, size;
+	size_t size;
 
 	oprom = pci_map_rom(pdev, &size);
 	if (!oprom)
 		return NULL;
 
 	/* Scour memory looking for the VBT signature. */
-	for (i = 0; i + 4 < size; i++) {
-		if (ioread32(oprom + i) != *((const u32 *)"$VBT"))
-			continue;
-
-		p = oprom + i;
-		size -= i;
-		break;
-	}
-
-	if (!p)
-		goto err_unmap_oprom;
+	for (p = oprom; size >= 4; p += 4, size -= 4)
+		if (ioread32(p) == *((const u32 *)"$VBT"))
+			break;
 
 	if (sizeof(struct vbt_header) > size) {
-		DRM_DEBUG_DRIVER("VBT header incomplete\n");
+		if (size >= 4)
+			DRM_DEBUG_DRIVER("VBT header incomplete\n");
 		goto err_unmap_oprom;
 	}
 
-- 
2.24.0