video and usb driver (rk3588)

[Stefan Kalkowski]

Hello Michael,

On Wed, Jan 18, 2023 at 02:39:25PM +0100, Michael Grunditz wrote:
> > I have a display now and it is really fast! However clipping doesn't
> > work as it should. It doesn't crash but it makes graphics a bit blurry
> > if active, and so is mouse pointer. There is no speed gain with
> > clipping.
> 
> 
> Solved! I had "CACHE" as attribute for the dma buffer. I changed to
> WRITE_COMBINED now, and it all works!
> Thanks to Norman who suggested cache problems.

I'm pretty sure that Norman did not want you to set the DMA buffer to
WRITE_COMBINED. Actually, this pseudo cache setting only exists for
historical reasons, and will get removed as soon as possible from the
public API. It is not really a 'cache feature'. It is not available on
ARM, but is simply mapped to UNCACHED.

That means you have set your DMA buffers to UNCACHED, which obviously
solves cache maintainance problems to the price of performance.

Regards
Stefan

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-- 
Stefan Kalkowski
Genode labs

https://github.com/skalk | https://genode.org