Re: [PATCH] drm/imx/ipuv3: do not adjust hactive for non-8-pixel-aligned modes

[Philipp Zabel <p.zabel@pengutronix.de>]

On Mo, 2026-04-06 at 17:36 +0200, Magnus Hörlin wrote:
> The IPUv3 display driver rounds up hactive to 8-pixel alignment in
> mode_set_nofb(), stealing pixels from the front porch.
> ipu_src_rect_width() applies the same rounding to the IDMAC read
> width. While this keeps the DC and IDMAC in sync, it causes the
> display to receive more active pixels than the mode specifies.
> 
> On fixed-pixel displays whose native width is not 8-pixel aligned
> (e.g. 854x480), the extra pixels cause visible skewing: each
> scanline is offset, making vertical lines lean.
> 
> Remove both alignment overrides. The IDMAC and DC now use the exact
> mode width.

This partially reverts 94dfec48fca7 ("drm/imx: Add 8 pixel alignment
fix") [1] without mentioning it, so I assume this patch breaks imx6dl-
b105pv2.

[1] https://lore.kernel.org/all/20210428222953.235280-6-sebastian.reichel@collabora.com/

> The DMA burst size is already adapted to arbitrary
> widths by ipu_calculate_bursts(), so no alignment is required at
> the pixel level.

The reference manual mentions burst size (NPB) has to be a multiple of
8 pixels at least for planar and semi-planar YUV formats. Without the
width alignment, ipu_calculate_bursts() doesn't guarantee this.

> Demote the DC warning about non-8-aligned hactive to dev_dbg, since
> it is informational rather than indicative of a problem.
> 
> Signed-off-by: Magnus Hörlin <magnus@alefors.se>

I wonder why the 8-pixel alignment check in ipu_di_adjust_videomode()
which has not been removed, doesn't cause ipu_crtc_mode_fixup() to
fail.

regards
Philipp