On 24/05/2026 23:33, Chen-Yu Tsai wrote: > Hi, > > (resent from new email) > > On Thu, May 14, 2026 at 2:04 PM Krzysztof Kozlowski <[email protected]> wrote: >> >> On Sat, May 09, 2026 at 09:00:14PM +0200, Jernej Skrabec wrote: >>> From: Jernej Skrabec <[email protected]> >>> >>> As it turns out, current H616 DE33 binding was written based on >>> incomplete understanding of DE33 design. Namely, planes are shared >>> resource and not tied to specific mixer, which was the case for previous >>> generations of Display Engine (DE3 and earlier). >>> >>> This means that current DE33 binding doesn't properly reflect HW and >>> using it would mean that second mixer (used for second display output) >>> can't be supported. >>> >>> Remove layer register space, which will be represented with additional >>> node, and replace it with phandle, which will point to that new, shared >>> node. That way, all mixers can share same layers. >>> >>> There is no user of this binding yet, so changes can be made safely, >>> without breaking any backward compatibility. >> >> There is user. git grep gives me: >> drivers/gpu/drm/sun4i/sun8i_mixer.c >> >> which means this is a released ABI. As I understood, the old code was > > We held off on merging the DT changes so that we could rework this. > I can't find the actual request though. It was probably over IRC. > >> working fine but just did not support all use cases. Why this cannot be >> kept backwards compatible? > > AFAIK the "planes" block is shared between two display mixers. As the > commit message explains, this prevents using the second mixer, since > only one of them can claim and map the register space. And on the H700 > (which is the same die as the H616 discussed here but with more exposed > interfaces), there could actually be a use case for the second mixer.
It explains why you want to make the changes but not why you cannot keep it backwards compatible. Best regards, Krzysztof
