On Wed, 20 Nov 2019, Lucas De Marchi <lucas.demarchi@xxxxxxxxx> wrote:
> 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 "$VBT".
>
> However when using ACPI it's guaranteed the VBT is 4-byte aligned
> per spec, so we can probably assume it here as well.
>
> Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_bios.c | 19 ++++++-------------
> 1 file changed, 6 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index aa9b182efee5..6bf57b1ad056 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -1902,27 +1902,20 @@ static struct vbt_header *oprom_get_vbt(struct drm_i915_private *dev_priv)
> void __iomem *p = NULL, *oprom;
> struct vbt_header *vbt;
> u16 vbt_size;
> - size_t i, size;
> + size_t size;
>
> oprom = pci_map_rom(pdev, &size);
> if (!oprom)
> return NULL;
>
> /* Scour memory looking for the VBT signature. */
> - for (i = 0; i + 4 < size; i++) {
> - if (ioread32(oprom + i) != *((const u32 *)"$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;
I think the original is easier to read. You only really need to change
"i++" to "i += 4" and be done with it.
BR,
Jani.
>
> 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;
> }
--
Jani Nikula, Intel Open Source Graphics Center
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