Re: [PATCH 3/5] drm/amdgpu/sdma5.2: adjust SDMA limits

[timur.kristof@gmail.com]

On Fri, 2025-09-12 at 15:38 -0400, Alex Deucher wrote:
> On Thu, Sep 11, 2025 at 2:18 PM Alex Deucher <alexdeucher@gmail.com>
> wrote:
> > 
> > On Thu, Sep 11, 2025 at 1:25 PM Alex Deucher
> > <alexander.deucher@amd.com> wrote:
> > > 
> > > SDMA 5.2.x has increased transfer limits.
> > > 
> > > v2: fix harder, use shifts to make it more obvious
> > > 
> > > Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> > > ---
> > >  drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c
> > > b/drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c
> > > index a8e39df29f343..bf227eadbe487 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/sdma_v5_2.c
> > > @@ -2065,11 +2065,11 @@ static void
> > > sdma_v5_2_emit_fill_buffer(struct amdgpu_ib *ib,
> > >  }
> > > 
> > >  static const struct amdgpu_buffer_funcs sdma_v5_2_buffer_funcs =
> > > {
> > > -       .copy_max_bytes = 0x400000,
> > > +       .copy_max_bytes = 1 << 30,
> > >         .copy_num_dw = 7,
> > >         .emit_copy_buffer = sdma_v5_2_emit_copy_buffer,
> > > 
> > > -       .fill_max_bytes = 0x400000,
> > > +       .fill_max_bytes = 1 << 30,
> > 
> > The hw docs and PAL differ here.  I've asked the hw designers to
> > clarify.
> 
> The HW team verified that the hardware supports the extended range
> for
> both copies and fills.
> 
> Alex

Hi Alex,

This is still pretty confusing.
According to PAL, only SDMA v6 has the extended range for fills, and it
can do 4 bytes fewer.

Are you sure that PAL is wrong about this?

For reference:
https://github.com/GPUOpen-Drivers/pal/blob/dev/src/core/hw/gfxip/sdma/gfx10/gfx10DmaCmdBuffer.cpp
https://github.com/GPUOpen-Drivers/pal/blob/dev/src/core/hw/gfxip/sdma/gfx12/gfx12DmaCmdBuffer.cpp

MaxCopySize on GFX10: 1 << 22
MaxCopySize on GFX10.3+: 1 << 30

MaxFillSize on GFX10-10.3: (1 << 22 - 1) & ~3
MaxFillSize on GFX11+: (1 << 30 - 1) & ~3
This makes sense because they program the count field in the packet
using the byte count minus four.

Thanks,
Timur