Re: [PATCH 1/2] drm/tegra: Support swapping chroma planes

[Mikko Perttunen]

On Friday, October 9, 2026 5:59 PM Mikko Perttunen wrote:
> On Friday, October 9, 2026 5:57 AM Aaron Kling via B4 Relay wrote:
> > From: Aaron Kling <webgeek1234@xxxxxxxxx>
> > 
> > The Tegra display controller supports some yuv types, but not their
> > chroma swapped variants. For example, yuv420 is supported but yvu420 is
> > not. This can be efficiently worked around by just passing the hardware
> > said chroma planes backwards. Add a flag to the plane state struct and
> > handling to both tegradc and nvdisplay paths.
> > 
> > Signed-off-by: Aaron Kling <webgeek1234@xxxxxxxxx>
> > ---
> >  drivers/gpu/drm/tegra/dc.c    | 17 ++++++++++++-----
> >  drivers/gpu/drm/tegra/hub.c   | 14 +++++++++-----
> >  drivers/gpu/drm/tegra/plane.c |  4 +++-
> >  drivers/gpu/drm/tegra/plane.h |  3 ++-
> >  4 files changed, 26 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> > index b0bfa946e6979..76d3841a17b8b 100644
> > --- a/drivers/gpu/drm/tegra/dc.c
> > +++ b/drivers/gpu/drm/tegra/dc.c
> > @@ -444,7 +444,8 @@ tegra_plane_use_vertical_filtering(struct tegra_plane *plane,
> >  }
> >  
> >  static void tegra_dc_setup_window(struct tegra_plane *plane,
> > -				  const struct tegra_dc_window *window)
> > +				  const struct tegra_dc_window *window,
> > +				  struct tegra_plane_state *tegra_plane_state)
> >  {
> >  	unsigned h_offset, v_offset, h_size, v_size, h_dda, v_dda, bpp;
> >  	struct tegra_dc *dc = plane->dc;
> > @@ -510,10 +511,13 @@ static void tegra_dc_setup_window(struct tegra_plane *plane,
> >  	tegra_plane_writel(plane, window->base[0], DC_WINBUF_START_ADDR);
> >  
> >  	if (yuv && planes > 1) {
> > -		tegra_plane_writel(plane, window->base[1], DC_WINBUF_START_ADDR_U);
> > +		uint8_t u = tegra_plane_state->swap_uv ? 2 : 1;
> > +		uint8_t v = tegra_plane_state->swap_uv ? 1 : 2;
> > +
> > +		tegra_plane_writel(plane, window->base[u], DC_WINBUF_START_ADDR_U);
> >  
> >  		if (planes > 2)
> > -			tegra_plane_writel(plane, window->base[2], DC_WINBUF_START_ADDR_V);
> > +			tegra_plane_writel(plane, window->base[v], DC_WINBUF_START_ADDR_V);
> >  
> >  		value = window->stride[1] << 16 | window->stride[0];
> >  		tegra_plane_writel(plane, value, DC_WIN_LINE_STRIDE);
> > @@ -740,7 +744,8 @@ static int tegra_plane_atomic_check(struct drm_plane *plane,
> >  
> >  	err = tegra_plane_format(new_plane_state->fb->format->format,
> >  				 &plane_state->format,
> > -				 &plane_state->swap);
> > +				 &plane_state->swap,
> > +				 &plane_state->swap_uv);
> >  	if (err < 0)
> >  		return err;
> >  
> > @@ -871,8 +876,10 @@ static void tegra_plane_atomic_update(struct drm_plane *plane,
> >  		if (i < 2)
> >  			window.stride[i] = fb->pitches[i];
> >  	}
> > +	if (tegra_plane_state->swap_uv)
> > +		window.stride[1] = fb->pitches[2];
> 
> Based on the comment above, U and V have the same stride, so this
> isn't required.
> 
> >  
> > -	tegra_dc_setup_window(p, &window);
> > +	tegra_dc_setup_window(p, &window, tegra_plane_state);
> 
> Instead of passing the plane state, I'd just add a
> 
>   swap(window.base[1], window.base[2]);
> 
> here.
> 
> Otherwise looks good to me! I also tested on AGX Xavier.
> 
> Mikko

(Well, sashiko has some findings, please check them as well)

> 
> >  }
> >  
> >  static const struct drm_plane_helper_funcs tegra_plane_helper_funcs = {
> > diff --git a/drivers/gpu/drm/tegra/hub.c b/drivers/gpu/drm/tegra/hub.c
> > index 448f49f3a7d7e..6427155ac4fdf 100644
> > --- a/drivers/gpu/drm/tegra/hub.c
> > +++ b/drivers/gpu/drm/tegra/hub.c
> > @@ -440,7 +440,8 @@ static int tegra_shared_plane_atomic_check(struct drm_plane *plane,
> >  
> >  	err = tegra_plane_format(new_plane_state->fb->format->format,
> >  				 &plane_state->format,
> > -				 &plane_state->swap);
> > +				 &plane_state->swap,
> > +				 &plane_state->swap_uv);
> >  	if (err < 0)
> >  		return err;
> >  
> > @@ -664,24 +665,27 @@ static void tegra_shared_plane_atomic_update(struct drm_plane *plane,
> >  	tegra_plane_writel(p, value, DC_WIN_PLANAR_STORAGE);
> >  
> >  	if (yuv && planes > 1) {
> > -		base = tegra_plane_state->iova[1] + fb->offsets[1];
> > +		uint8_t u = tegra_plane_state->swap_uv ? 2 : 1;
> > +		uint8_t v = tegra_plane_state->swap_uv ? 1 : 2;
> > +
> > +		base = tegra_plane_state->iova[u] + fb->offsets[u];
> >  		base |= addr_flag;
> >  
> >  		tegra_plane_writel(p, upper_32_bits(base), DC_WINBUF_START_ADDR_HI_U);
> >  		tegra_plane_writel(p, lower_32_bits(base), DC_WINBUF_START_ADDR_U);
> >  
> >  		if (planes > 2) {
> > -			base = tegra_plane_state->iova[2] + fb->offsets[2];
> > +			base = tegra_plane_state->iova[v] + fb->offsets[v];
> >  			base |= addr_flag;
> >  
> >  			tegra_plane_writel(p, upper_32_bits(base), DC_WINBUF_START_ADDR_HI_V);
> >  			tegra_plane_writel(p, lower_32_bits(base), DC_WINBUF_START_ADDR_V);
> >  		}
> >  
> > -		value = PITCH_U(fb->pitches[1]);
> > +		value = PITCH_U(fb->pitches[u]);
> >  
> >  		if (planes > 2)
> > -			value |= PITCH_V(fb->pitches[2]);
> > +			value |= PITCH_V(fb->pitches[v]);
> >  
> >  		tegra_plane_writel(p, value, DC_WIN_PLANAR_STORAGE_UV);
> >  	} else {
> > diff --git a/drivers/gpu/drm/tegra/plane.c b/drivers/gpu/drm/tegra/plane.c
> > index 2148b0c59815c..f4feec62ac023 100644
> > --- a/drivers/gpu/drm/tegra/plane.c
> > +++ b/drivers/gpu/drm/tegra/plane.c
> > @@ -319,11 +319,13 @@ int tegra_plane_state_add(struct tegra_plane *plane,
> >  	return 0;
> >  }
> >  
> > -int tegra_plane_format(u32 fourcc, u32 *format, u32 *swap)
> > +int tegra_plane_format(u32 fourcc, u32 *format, u32 *swap, bool *swap_uv)
> >  {
> >  	/* assume no swapping of fetched data */
> >  	if (swap)
> >  		*swap = BYTE_SWAP_NOSWAP;
> > +	if (swap_uv)
> > +		*swap_uv = false;
> >  
> >  	switch (fourcc) {
> >  	case DRM_FORMAT_ARGB4444:
> > diff --git a/drivers/gpu/drm/tegra/plane.h b/drivers/gpu/drm/tegra/plane.h
> > index e33a581e6490e..dba5f1b254e98 100644
> > --- a/drivers/gpu/drm/tegra/plane.h
> > +++ b/drivers/gpu/drm/tegra/plane.h
> > @@ -49,6 +49,7 @@ struct tegra_plane_state {
> >  	struct tegra_bo_tiling tiling;
> >  	u32 format;
> >  	u32 swap;
> > +	bool swap_uv;
> >  
> >  	bool reflect_x;
> >  	bool reflect_y;
> > @@ -88,7 +89,7 @@ void tegra_plane_cleanup_fb(struct drm_plane *plane,
> >  int tegra_plane_state_add(struct tegra_plane *plane,
> >  			  struct drm_plane_state *state);
> >  
> > -int tegra_plane_format(u32 fourcc, u32 *format, u32 *swap);
> > +int tegra_plane_format(u32 fourcc, u32 *format, u32 *swap, bool *swap_uv);
> >  bool tegra_plane_format_is_indexed(unsigned int format);
> >  bool tegra_plane_format_is_yuv(unsigned int format, unsigned int *planes, unsigned int *bpc);
> >  int tegra_plane_setup_legacy_state(struct tegra_plane *tegra,
> > 
> > -- 
> > 2.54.0
> > 
> > 
> > 
> 
> 
> 
>