[PATCH 00/26] x86: video: Speed up the framebuffer

Simon Glass
2020-05-22T23:13:27Z

Hi Bin,

On Fri, 22 May 2020 at 17:09, Bin Meng <bmeng.cn@gmail.com> wrote:
>
> Hi Simon,
>
> On Sat, May 23, 2020 at 12:34 AM Simon Glass <sjg@chromium.org> wrote:
> >
> > Hi Bin,
> >
> > On Fri, 22 May 2020 at 09:30, Bin Meng <bmeng.cn@gmail.com> wrote:
> > >
> > > Hi Simon,
> > >
> > > On Wed, May 20, 2020 at 7:11 AM Simon Glass <sjg@chromium.org> wrote:
> > > >
> > > > Some architectures use a cached framebuffer and flush the cache as needed
> > > > so that changes are visible. This is supported by U-Boot.
> > > >
> > > > However x86 uses an uncached framebuffer with a 'write-combining' feature
> > > > to speed up writes. Reads are permitted but they are extremely expensive.
> > > >
> > >
> > > Is it possible to use cached framebuffer on x86?
> >
> > It might be possible on newer chips. I see so much conflicting stuff
> > about flushing the cache, though. The write-through cache is slow for
> > reads. The write-back cache never writes unless you flush.
>
> But you said "This is supported by U-Boot." So if we use cached frame
> buffers on x86, the video driver already handles the cache coherency
> for us? Not sure what conflicting stuff did you see?

It is supported by U-Boot on ARM.

If you enable write-back caching, you see nothing on the display. I
did try that, but no dice.

Regards,
Simon

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