On Mon, Sep 23, 2024 at 12:12:39PM +0300, Jani Nikula wrote:
> On Fri, 20 Sep 2024, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> > On Thu, Sep 12, 2024 at 03:15:52PM +0300, Jani Nikula wrote:
> >> On Tue, 10 Sep 2024, Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> >> > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> >> >
> >> > Replace the three hand rolled "$VBT"s with a vbt_signature[]
> >> > to avoid accidents.
> >> >
> >> > Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> >> > ---
> >> > drivers/gpu/drm/i915/display/intel_bios.c | 12 +++++++++---
> >> > 1 file changed, 9 insertions(+), 3 deletions(-)
> >> >
> >> > diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> >> > index cbbda94c3dab..0b92b494117f 100644
> >> > --- a/drivers/gpu/drm/i915/display/intel_bios.c
> >> > +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> >> > @@ -2964,6 +2964,8 @@ static const struct bdb_header *get_bdb_header(const struct vbt_header *vbt)
> >> > return _vbt + vbt->bdb_offset;
> >> > }
> >> >
> >> > +static const char vbt_signature[4] = "$VBT";
> >>
> >> Always a bit scary to add strings without termination, but I guess it's
> >> justified here.
> >
> > I guess we could make it look less like a string with eg.
> > static const u8 vbt_signature[] = { '$', 'V', 'B', 'T' };
> > ?
>
> Alternatively,
>
> static const char *vbt_signature = "$VBT";
Or could just be something like:
static const char vbt_signature[] = "$VBT";
static const int vbt_signature_len = 4;
BUILD_BUG_ON(vbt_signature_len != sizeof(vbt_signature) - 1);
BUILD_BUG_ON(vbt_signature_len != sizeof(u32));
and use vbt_signature_len instead sizeof(vbt_signature) everwhere.
>
> >
> >> Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> >>
> >>
> >> > +
> >> > /**
> >> > * intel_bios_is_valid_vbt - does the given buffer contain a valid VBT
> >> > * @display: display device
> >> > @@ -2986,7 +2988,7 @@ bool intel_bios_is_valid_vbt(struct intel_display *display,
> >> > return false;
> >> > }
> >> >
> >> > - if (memcmp(vbt->signature, "$VBT", 4)) {
> >> > + if (memcmp(vbt->signature, vbt_signature, sizeof(vbt_signature))) {
>
> But then this would need strlen()
>
> >> > 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));
>
> And maybe this could be sizeof(vbt_signature) < sizeof(u32)
>
> All of the alternatives are a bit disappointing, so maybe let's just
> roll with the patch you already have here?
>
> BR,
> Jani.
>
> >> > +
> >> > 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
>
> --
> Jani Nikula, Intel
--
Ville Syrjälä
Intel
