Re: [PATCH] drm/sysfb: ofdrm: Fix is_avivo() constant comparison bug

[Thomas Zimmermann]

Hi

Am 24.07.26 um 15:21 schrieb Shixiong Ou:
> On 2026/7/24 19:34, Thomas Zimmermann wrote:
> > Hi
> >
> > Am 24.07.26 um 11:41 schrieb oushixiong1025@xxxxxxx:
> > > From: Shixiong Ou <oushixiong@xxxxxxxxxx>
> > >
> > > The is_avivo() function has a logic error where it compares a constant
> > > to another constant instead of checking the device parameter:
> > >
> > >    (PCI_VENDOR_ID_ATI_R600 >= 0x9400)
> > >
> > > However, according to the code comment and the OFDRM_MODEL_AVIVO
> > > definition ("ATI R5xx"), this function is intended to match only R5xx
> > > cards (device IDs 0x7100-0x7800), not R6xx or later. The second
> > > condition checking for R600 is erroneous and should be removed.
> > >
> > > Signed-off-by: Shixiong Ou <oushixiong@xxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/sysfb/ofdrm.c | 3 +--
> > >   1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/sysfb/ofdrm.c 
> > > b/drivers/gpu/drm/sysfb/ofdrm.c
> > > index a6dc34b9ec0f..ea1db1cfe3ed 100644
> > > --- a/drivers/gpu/drm/sysfb/ofdrm.c
> > > +++ b/drivers/gpu/drm/sysfb/ofdrm.c
> > > @@ -238,8 +238,7 @@ static bool is_avivo(u32 vendor, u32 device)
> > >   {
> > >       /* This will match most R5xx */
> > >       return (vendor == PCI_VENDOR_ID_ATI) &&
> > > -           ((device >= PCI_VENDOR_ID_ATI_R520 && device < 0x7800) ||
> > > -        (PCI_VENDOR_ID_ATI_R600 >= 0x9400));
> >
> > I tried to match exactly this: 
> > https://elixir.bootlin.com/linux/v7.1.4/source/drivers/video/fbdev/offb.c#L365
> >
> > IDK if that works in practice, but I don't dare changing it without a 
> > concrete bug report.
> >
> > Best regards
> > Thomas
> Hi,
>
> PCI_VENDOR_ID_ATI_R600 is defined as 0x9400 . Therefore, this 
> expression always evaluates to true (0x9400 >= 0x9400).
> It does not depend on the device parameter passed to is_avivo().
> So is this a coding mistake?

Oh, now I see it. That's indeed a bug. It should test for (device >= 
PCI_VENDOR_ID_ATI_R600) instead.  Thanks for addressing this.

Best regards
Thomas


> Best regards
> Shixiong Ou.
>
> > > +           (device >= PCI_VENDOR_ID_ATI_R520 && device < 0x7800);
> > >   }
> > >     static enum ofdrm_model display_get_model_of(struct drm_device 
> > > *dev, struct device_node *of_node)

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)