vc4_bo_create: Failed to allocate from CMA

[Daniel Stone]

On Thu, 17 Jun 2021 at 10:36, nicolas saenz julienne <nsaenz at kernel.org> wrote:
> Frankly I don't know if there is a better way. IIRC opensuse and downstream use
> DT overlays to cater for this limitation. It seems reasonable to bump the
> value. But it'll be in detriment of users that don't care much for graphical
> interfaces. Nonetheless, I'm not familiar with how DRM handles CMA/DMA memory.
> So let me have a look at it. Maybe there is a SW fix. At first glance I'm
> surprised they can't defer to normal page allocations when CMA isn't capable of
> honoring the request (like the dma code does).

DMA transfers can be split into multiple transactions at the cost of
being a bit slower. But there isn't a fallback for graphics buffers;
you can't display a quarter of a screen at a time. If the hardware did
support buffers being backed by multiple discontiguous pages, then it
wouldn't need CMA in the first place ...

Cheers,
Daniel