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";
>
>> 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
