Re: [PATCH 2/2] drm/nouveau: DRM_NOUVEAU_SET_ZCULL_CTXSW_BUFFER

[Danilo Krummrich <dakr@kernel.org>]

On Fri, Mar 21, 2025 at 07:00:57PM -0400, M Henning wrote:
> This is a pointer in the gpu's virtual address space. It must be
> aligned according to ctxsw_align and be at least ctxsw_size bytes
> (where those values come from the nouveau_abi16_ioctl_get_zcull_info
> structure). I'll change the description to say that much.
> 
> Yes, this is GEM-backed. I'm actually not entirely sure what the
> requirements are here, since this part is reverse-engineered. I think
> NOUVEAU_GEM_DOMAIN_VRAM and NOUVEAU_GEM_DOMAIN_GART are both okay. The
> proprietary driver allocates this buffer using
> NV_ESC_RM_VID_HEAP_CONTROL and sets attr = NVOS32_ATTR_LOCATION_ANY |
> NVOS32_ATTR_PAGE_SIZE_BIG | NVOS32_ATTR_PHYSICALITY_CONTIGUOUS, attr2
> = NVOS32_ATTR2_GPU_CACHEABLE_YES | NVOS32_ATTR2_ZBC_PREFER_NO_ZBC.

(Please do not top post.)

What I mean is how do you map the backing GEM into the GPU's virtual address
space? Since it's bound to a channel, I assume that it must be ensured it's
properly mapped when work is pushed to the channel. Is it mapped through
VM_BIND?

> 
> On Thu, Mar 20, 2025 at 2:34 PM Danilo Krummrich <dakr@kernel.org> wrote:
> >
> > On Wed, Mar 12, 2025 at 05:36:15PM -0400, Mel Henning wrote:
> > > diff --git a/include/uapi/drm/nouveau_drm.h b/include/uapi/drm/nouveau_drm.h
> >
> > Same here, please split the uAPI change in a separate commit.
> >
> > > index 33361784eb4e..e9638f4dd7e6 100644
> > > --- a/include/uapi/drm/nouveau_drm.h
> > > +++ b/include/uapi/drm/nouveau_drm.h
> > > @@ -448,6 +448,20 @@ struct drm_nouveau_get_zcull_info {
> > >       __u32 ctxsw_align;
> > >  };
> > >
> > > +struct drm_nouveau_set_zcull_ctxsw_buffer {
> > > +     /**
> > > +      * @ptr: The virtual address for the buffer, or null to bind nothing
> > > +      */
> > > +     __u64 addr;
> >
> > What is this buffer? Is this a GEM object backed buffer? How is it mapped?
> >
> > > +
> > > +     /**
> > > +      * @channel: the channel to set the buffer on
> > > +      */
> > > +     __u32 channel;
> > > +
> > > +     __u32 pad;
> > > +};
> > > +
> > >  #define DRM_NOUVEAU_GETPARAM           0x00
> > >  #define DRM_NOUVEAU_SETPARAM           0x01 /* deprecated */
> > >  #define DRM_NOUVEAU_CHANNEL_ALLOC      0x02
> > > @@ -462,6 +476,7 @@ struct drm_nouveau_get_zcull_info {
> > >  #define DRM_NOUVEAU_VM_BIND            0x11
> > >  #define DRM_NOUVEAU_EXEC               0x12
> > >  #define DRM_NOUVEAU_GET_ZCULL_INFO     0x13
> > > +#define DRM_NOUVEAU_SET_ZCULL_CTXSW_BUFFER 0x14
> > >  #define DRM_NOUVEAU_GEM_NEW            0x40
> > >  #define DRM_NOUVEAU_GEM_PUSHBUF        0x41
> > >  #define DRM_NOUVEAU_GEM_CPU_PREP       0x42
> > > @@ -532,6 +547,7 @@ struct drm_nouveau_svm_bind {
> > >  #define DRM_IOCTL_NOUVEAU_EXEC               DRM_IOWR(DRM_COMMAND_BASE + DRM_NOUVEAU_EXEC, struct drm_nouveau_exec)
> > >
> > >  #define DRM_IOCTL_NOUVEAU_GET_ZCULL_INFO     DRM_IOR (DRM_COMMAND_BASE + DRM_NOUVEAU_GET_ZCULL_INFO, struct drm_nouveau_get_zcull_info)
> > > +#define DRM_IOCTL_NOUVEAU_SET_ZCULL_CTXSW_BUFFER  DRM_IOW (DRM_COMMAND_BASE + DRM_NOUVEAU_SET_ZCULL_CTXSW_BUFFER, struct drm_nouveau_set_zcull_ctxsw_buffer)
> > >  #if defined(__cplusplus)
> > >  }
> > >  #endif
> > > --
> > > 2.48.1
> > >