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[46.122.102.118]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4994dfe8973sm19187475e9.7.2026.08.04.10.58.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Aug 2026 10:58:47 -0700 (PDT) From: Jernej =?UTF-8?B?xaBrcmFiZWM=?= To: wens@kernel.org Cc: maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch, samuel@sholland.org, dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH 13/13] drm/sun4i: Align VI buffer addresses for subsampled formats Date: Tue, 04 Aug 2026 19:58:45 +0200 Message-ID: <58Gvon3UR1Sy7a6nLT6bDw@gmail.com> In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Dne torek, 4. avgust 2026 ob 19:04:10 Srednjeevropski poletni =C4=8Das je C= hen-Yu Tsai napisal(a): > On Wed, Aug 5, 2026 at 12:25=E2=80=AFAM Jernej =C5=A0krabec wrote: > > > > Dne torek, 4. avgust 2026 ob 13:14:38 Srednjeevropski poletni =C4=8Das = je Chen-Yu Tsai napisal(a): > > > On Tue, Aug 4, 2026 at 1:25=E2=80=AFAM Chen-Yu Tsai = wrote: > > > > > > > > On Tue, Aug 4, 2026 at 12:11=E2=80=AFAM Jernej Skrabec wrote: > > > > > > > > > > This is a partial revert of commit 79ac1c945ab8 ("drm/sun4i: laye= rs: > > > > > Use drm_fb_dma_get_gem_addr() to get display memory"). > > > > > > > > > > Chroma must start at the beginning of a subsampling block, for ex= ample > > > > > chroma start address for NV12 must be aligned to 2 pixels. > > > > > drm_fb_dma_get_gem_addr() offsets luma by the exact source coordi= nates > > > > > and chroma by the coordinates divided by the subsampling factor, = so for > > > > > odd offsets both planes no longer describe the same pixel, which = the > > > > > Display Engine scaler can't handle. > > > > > > > > > > Align source coordinates down for all planes instead. Remaining s= hift > > > > > of one pixel is already compensated with scaler phase shift in > > > > > sun8i_vi_layer_update_coord(). > > > > > > > > Well I think this applies to the format in general, and probably sh= ould > > > > be fixed in drm_fb_dma_get_gem_addr() instead? > > > > > > > > > Fixes: 79ac1c945ab8 ("drm/sun4i: layers: Use drm_fb_dma_get_gem_a= ddr() to get display memory") > > > > > Signed-off-by: Jernej Skrabec > > > > > --- > > > > > drivers/gpu/drm/sun4i/sun8i_vi_layer.c | 20 ++++++++++++++++++-- > > > > > 1 file changed, 18 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/drivers/gpu/drm/sun4i/sun8i_vi_layer.c b/drivers/gpu= /drm/sun4i/sun8i_vi_layer.c > > > > > index 09f668c8af24..ad036cb9d88e 100644 > > > > > --- a/drivers/gpu/drm/sun4i/sun8i_vi_layer.c > > > > > +++ b/drivers/gpu/drm/sun4i/sun8i_vi_layer.c > > > > > @@ -197,15 +197,31 @@ static void sun8i_vi_layer_update_buffer(st= ruct sun8i_layer *layer, > > > > > struct drm_plane_state *state =3D plane->state; > > > > > struct drm_framebuffer *fb =3D state->fb; > > > > > const struct drm_format_info *format =3D fb->format; > > > > > + struct drm_gem_dma_object *gem; > > > > > + u32 dx, dy, src_x, src_y; > > > > > dma_addr_t dma_addr; > > > > > u32 ch_base; > > > > > int i; > > > > > > > > > > ch_base =3D sun8i_channel_base(layer); > > > > > > > > > > + /* Adjust x and y to be divisible by subsampling factor */ > > > > > + src_x =3D (state->src.x1 >> 16) & ~(format->hsub - 1); > > > > > + src_y =3D (state->src.y1 >> 16) & ~(format->vsub - 1); > > > > > > > > AFAICT the only difference compared to drm_fb_dma_get_gem_addr() > > > > is the masking here, i.e. round_down(). > > > > > > > > > + > > > > > for (i =3D 0; i < format->num_planes; i++) { > > > > > - /* Get the start of the displayed memory */ > > > > > - dma_addr =3D drm_fb_dma_get_gem_addr(fb, state, i= ); > > > > > + gem =3D drm_fb_dma_get_gem_obj(fb, i); > > > > > + dma_addr =3D gem->dma_addr + fb->offsets[i]; > > > > > + > > > > > + dx =3D src_x; > > > > > + dy =3D src_y; > > > > > + if (i > 0) { > > > > > + dx /=3D format->hsub; > > > > > + dy /=3D format->vsub; > > > > > + } > > > > > + > > > > > + dma_addr +=3D dx * format->cpp[i]; > > > > > + dma_addr +=3D dy * fb->pitches[i]; > > > > > > > > > > > > Where as the helper has (or used to have before the blocksize stuff= ): > > > > > > > > paddr +=3D (format->cpp[plane] * (state->src_x >> 16)) / fb->fo= rmat->hsub; > > > > paddr +=3D (fb->pitches[plane] * (state->src_y >> 16)) / fb->fo= rmat->vsub; > > > > > > > > Am I missing something? > > > > > > After some headbanging on my end I see that the offset for the Y plane > > > needs to be rounded down. > > > > > > But instead of reverting the whole thing and open-coding the helper > > > again, could you adjust the address returned by the helper for odd > > > offsets? > > > > Yes, that's also an option. I'll do it in v2. > > > > > > > > And just a heads up, this also needs a clipped version of > > > drm_fb_dma_get_gem_addr() as sun8i_ui_layer_update_coord() uses the > > > clipped dimensions. I am currently working on this part. > > > > Can you explain a bit more? I don't see why it needs any adjustement. >=20 > My understanding is that drm_atomic_helper_check_plane_state() calculates > the "clipped" rectangles for the plane using values from userspace in > state->src_[xywh] and state->crtc_[xywh] and puts them in state->src > and state->dst, respectively. If the overlay is moved partially outside > the screen, the overlay is "clipped". >=20 >=20 > Say we have a screen of 1920x1080, with an overlay buffer that is 1280x72= 0. > Say state->src_x and state->src_y are (-50, 0), given by userspace. > drm_atomic_helper_check_plane_state() will calculate the clipped & scaled > rectangles and put them in state->src. This latter rectangle is what is > used sun8i_ui_layer_update_coord(). >=20 > So we would have: >=20 > (src_x, src_y) =3D (-50, 0), (src_w, src_h) =3D (1280, 720) >=20 > The clipped numbers are >=20 > (src.x1, src.y1) =3D (0, 0), (src.x2, src.y2) =3D (1230, 720) >=20 > src, not src_[xywh], is what sun8i layers uses to program the coordinates, > and prior to the drm_fb_dma_get_gem_addr() conversion, also to calculate > the buffer start address. drm_fb_dma_get_gem_addr() however uses src_[xy] > to calculate the address. >=20 >=20 > Essentially, when overlaying a clipped plane, the start address needs to > be adjusted if the source (top left) offset is outside the screen. > clipping =3D=3D automatic cropping to fit the screen. >=20 > I don't know if userspace applications routinely do this, but I think this > needs to be restored to the prior behavior. Uh, it would be nice if this is fixed. But I think it's not too common for app to use negative coordinates. Best regards, Jernej