Nouveau - Apr 2014 - [PATCH] drm/nouveau/bios: fix a bit shift error introduced by 457e77b

Commit 457e77b26428ab4a24998eecfb99f27fa4195397 added two checks applied to a
value received from nv_rd32(bios, 0x619f04). But after this new piece of code
is executed, the addr local variable does not hold the same value it used to
hold before the commit. Here is what is was assigned in the original code:
	(u64)(nv_rd32(bios, 0x619f04) & 0xffffff00) << 8
in the committed code it ends up with this value:
	(u64)(nv_rd32(bios, 0x619f04) >> 8) << 8
These expressions are obviously not equivalent.

My Nvidia video card does not show anything on the display when I boot a
kernel containing this commit.

The patch fixes the code so that the new checks are still done, but the
side effect of an incorrect addr value is gone.

Cc: Ben Skeggs <bskeggs at redhat.com>
Cc: Dave Airlie <airlied at redhat.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Sergei Antonov <saproj at gmail.com>
---
 drivers/gpu/drm/nouveau/core/subdev/bios/base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/core/subdev/bios/base.c
b/drivers/gpu/drm/nouveau/core/subdev/bios/base.c
index e9df94f..291adb6 100644
--- a/drivers/gpu/drm/nouveau/core/subdev/bios/base.c
+++ b/drivers/gpu/drm/nouveau/core/subdev/bios/base.c
@@ -109,7 +109,7 @@ nouveau_bios_shadow_pramin(struct nouveau_bios *bios)
 			return;
 		}
 
-		addr = (u64)(addr >> 8) << 8;
+		addr = (u64)(addr & 0xffffff00) << 8;
 		if (!addr) {
 			addr  = (u64)nv_rd32(bios, 0x001700) << 16;
 			addr += 0xf0000;
-- 
1.9.0

On 15 April 2014 23:18, Sergei Antonov <saproj at gmail.com>
wrote:
> Commit 457e77b26428ab4a24998eecfb99f27fa4195397 added two checks applied to
a
> value received from nv_rd32(bios, 0x619f04). But after this new piece of
code
> is executed, the addr local variable does not hold the same value it used
to
> hold before the commit. Here is what is was assigned in the original code:
>         (u64)(nv_rd32(bios, 0x619f04) & 0xffffff00) << 8
> in the committed code it ends up with this value:
>         (u64)(nv_rd32(bios, 0x619f04) >> 8) << 8
> These expressions are obviously not equivalent.
>
> My Nvidia video card does not show anything on the display when I boot a
> kernel containing this commit.
>
> The patch fixes the code so that the new checks are still done, but the
> side effect of an incorrect addr value is gone.
>
> Cc: Ben Skeggs <bskeggs at redhat.com>
> Cc: Dave Airlie <airlied at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Sergei Antonov <saproj at gmail.com>
> ---
>  drivers/gpu/drm/nouveau/core/subdev/bios/base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/core/subdev/bios/base.c
b/drivers/gpu/drm/nouveau/core/subdev/bios/base.c
> index e9df94f..291adb6 100644
> --- a/drivers/gpu/drm/nouveau/core/subdev/bios/base.c
> +++ b/drivers/gpu/drm/nouveau/core/subdev/bios/base.c
> @@ -109,7 +109,7 @@ nouveau_bios_shadow_pramin(struct nouveau_bios *bios)
>                         return;
>                 }
>
> -               addr = (u64)(addr >> 8) << 8;
> +               addr = (u64)(addr & 0xffffff00) << 8;
I just noticed that "(u64)" is redundant here. Can it be removed in
the patch without resubmitting, Andrew?
>                 if (!addr) {
>                         addr  = (u64)nv_rd32(bios, 0x001700) << 16;
>                         addr += 0xf0000;
> --
> 1.9.0
>

On 15/04/14 22:49, Sergei Antonov wrote:
> On 15 April 2014 23:18, Sergei Antonov <saproj at gmail.com> wrote:
>> Commit 457e77b26428ab4a24998eecfb99f27fa4195397 added two checks
applied to a
>> value received from nv_rd32(bios, 0x619f04). But after this new piece
of code
>> is executed, the addr local variable does not hold the same value it
used to
>> hold before the commit. Here is what is was assigned in the original
code:
>>         (u64)(nv_rd32(bios, 0x619f04) & 0xffffff00) << 8
>> in the committed code it ends up with this value:
>>         (u64)(nv_rd32(bios, 0x619f04) >> 8) << 8
>> These expressions are obviously not equivalent.
>>
>> My Nvidia video card does not show anything on the display when I boot
a
>> kernel containing this commit.
>>
>> The patch fixes the code so that the new checks are still done, but the
>> side effect of an incorrect addr value is gone.
>>
Hi Sergei

A similar patch [1] has been sent a few days prior to yours, and I'm
assuming
it will be queued/merged shortly. Just letting you know.

Cheers
-Emil

[1] http://lists.freedesktop.org/archives/dri-devel/2014-April/057318.html