Re: [PATCH] drm/amdgpu/userq: fix struct drm_amdgpu_info_device padding for 32bit compile

AMD General

Hi Alex,

I am not changing the layout.

For 64 bit gcc, default alignment for __u64 is 8bytes.
For 32 bit gcc, default alignment for __u64 is 4bytes.

For 32 bit gcc, I have manually padded 4bytes so that it is 8bytes aligned for __u64. This will make 64bit kernel compatible with 32bit mesa compiled using gcc.

Thank you,
Yogesh

________________________________
From: Alex Deucher <[email protected]>
Sent: Thursday, August 20, 2026 8:51 PM
To: Mohan Marimuthu, Yogesh <[email protected]>
Cc: [email protected] <[email protected]>; Deucher, Alexander <[email protected]>; Koenig, Christian <[email protected]>; Khatri, Sunil <[email protected]>
Subject: Re: [PATCH] drm/amdgpu/userq: fix struct drm_amdgpu_info_device padding for 32bit compile

On Thu, Aug 20, 2026 at 11:18 AM Mohan Marimuthu, Yogesh
<[email protected]> wrote:
>
> AMD General
>
> Hi Alex,
>
> In 32bit mesa, I did not get the correct userq_ip_mask value.
> I checked for variable alignment and tcc_disabled_mask was not on 8 byte alignment. This patch fixes it.
>
> Can you please tell how it would break UAPI. What did I miss.

You are changing the layout of the structure that existing apps expect.

Alex

>
> Thank you,
> Yogesh
>
> ________________________________
> From: Alex Deucher <[email protected]>
> Sent: Thursday, August 20, 2026 7:23 PM
> To: Mohan Marimuthu, Yogesh <[email protected]>
> Cc: [email protected] <[email protected]>; Deucher, Alexander <[email protected]>; Koenig, Christian <[email protected]>; Khatri, Sunil <[email protected]>
> Subject: Re: [PATCH] drm/amdgpu/userq: fix struct drm_amdgpu_info_device padding for 32bit compile
>
> On Thu, Aug 20, 2026 at 12:55 AM Yogesh Mohan Marimuthu
> <[email protected]> wrote:
> >
> > need to pad before __u64 tcc_disabled_mask variable.
> >
> > Signed-off-by: Yogesh Mohan Marimuthu <[email protected]>
>
> This will break UAPI.
>
> Alex
>
> > ---
> >  include/uapi/drm/amdgpu_drm.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/uapi/drm/amdgpu_drm.h b/include/uapi/drm/amdgpu_drm.h
> > index 0a113529b..5beef3eaa 100644
> > --- a/include/uapi/drm/amdgpu_drm.h
> > +++ b/include/uapi/drm/amdgpu_drm.h
> > @@ -1517,6 +1517,7 @@ struct drm_amdgpu_info_device {
> >         __u64 high_va_max;
> >         /* gfx10 pa_sc_tile_steering_override */
> >         __u32 pa_sc_tile_steering_override;
> > +       __u32 pad;
> >         /* disabled TCCs */
> >         __u64 tcc_disabled_mask;
> >         __u64 min_engine_clock;
> > @@ -1541,7 +1542,6 @@ struct drm_amdgpu_info_device {
> >         __u32 csa_alignment;
> >         /* Userq IP mask (1 << AMDGPU_HW_IP_*) */
> >         __u32 userq_ip_mask;
> > -       __u32 pad;
> >  };
> >
> >  struct drm_amdgpu_info_hw_ip {
> > --
> > 2.43.0
> >