Re: [PATCH] drm: mxsfb: lcdif: enforce 64-byte pitch alignment for scanout

[Advait Dhamorikar]

Hello Philipp,

> I wonder if setting 4320 bytes stride works if you reduce the burst
> size, for example by reverting commit 2215cb3be5c2 ("drm: lcdif: change
> burst size to 256B") to test.

Unfortunately, reverting the commit doesn't seem to fix the issue.
I tested with the reduced/default burst size as well as explicitly
setting it to 128 bytes, but a pitch of 4320 bytes still results in a
corrupted output(stretched and choppy display).

However, using a 64 byte aligned pitch works in all cases without having
to alter the burst size.

Best regards,
Advait

On Mon, Apr 13, 2026 at 7:16 PM Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote:
>
> Hi,
>
> On Mo, 2026-04-13 at 17:14 +0530, Advait Dhamorikar wrote:
> > The LCDIF controller expects framebuffer pitch to be aligned to a
> > 64 byte boundary for reliable scanout.
> >
> > While byte-granular pitches are
> > supported by the interface, the i.MX8MP reference manual
> > recommends 64-byte alignment for optimal operation.
> >
> > Corrupted output was observed with XR24 framebuffers where a pitch of
> > 4320 bytes caused visible corruption and choppy display, while an aligned
> > pitch of 4352 bytes worked correctly.
>
> This happens to be divisible by 256, which is is the burst size
> currently set in the undocumented CTRLDESCL0_3 register fields,
> according to the comment in lcdif_set_mode().
>
> I wonder if setting 4320 bytes stride works if you reduce the burst
> size, for example by reverting commit 2215cb3be5c2 ("drm: lcdif: change
> burst size to 256B") to test.
>
> If that is the case, it might be better to allow unaligned pitches but
> configure the burst size depending on pitch alignment.
>
> regards
> Philipp