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

[Joel Stanley]

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>

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);
>         }