drivers/gpu/drm/ast: Fix infinite loop if read fails

[Daniel Vetter]

On Fri, Dec 16, 2016 at 11:38:57AM +1030, Joel Stanley wrote:
> On Thu, Dec 15, 2016 at 3:42 PM, Russell Currey <ruscur at russell.cc> wrote:
> > ast_get_dram_info() configures a window in order to access BMC memory.
> > A BMC register can be configured to disallow this, and if so, causes
> > an infinite loop in the ast driver which renders the system unusable.
> >
> > Fix this by erroring out if an error is detected.  On powerpc systems with
> > EEH, this leads to the device being fenced and the system continuing to
> > operate.
> >
> > Cc: <stable at vger.kernel.org> # 3.10+
> > Signed-off-by: Russell Currey <ruscur at russell.cc>
> 
> Reviewed-by: Joel Stanley <joel at jms.id.au>

Applied to drm-misc-fixes.
-Daniel

> 
> Thanks Russel.
> 
> Cheers,
> 
> Joel
> 
> 
> > ---
> >  drivers/gpu/drm/ast/ast_main.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
> > index 904beaa..f75c642 100644
> > --- a/drivers/gpu/drm/ast/ast_main.c
> > +++ b/drivers/gpu/drm/ast/ast_main.c
> > @@ -223,7 +223,8 @@ static int ast_get_dram_info(struct drm_device *dev)
> >         ast_write32(ast, 0x10000, 0xfc600309);
> >
> >         do {
> > -               ;
> > +               if (pci_channel_offline(dev->pdev))
> > +                       return -EIO;
> >         } while (ast_read32(ast, 0x10000) != 0x01);
> >         data = ast_read32(ast, 0x10004);
> >
> > @@ -428,7 +429,9 @@ int ast_driver_load(struct drm_device *dev, unsigned long flags)
> >         ast_detect_chip(dev, &need_post);
> >
> >         if (ast->chip != AST1180) {
> > -               ast_get_dram_info(dev);
> > +               ret = ast_get_dram_info(dev);
> > +               if (ret)
> > +                       goto out_free;
> >                 ast->vram_size = ast_get_vram_info(dev);
> >                 DRM_INFO("dram %d %d %d %08x\n", ast->mclk, ast->dram_type, ast->dram_bus_width, ast->vram_size);
> >         }
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch