[RFC PATCH 1/9] usb: xhci: Add missing cache flush in the scratchpad array initialization

[Simon Glass]

On Wed, 22 Apr 2020 at 06:33, Nicolas Saenz Julienne
<nsaenzjulienne at suse.de> wrote:
>
> On Wed, 2020-04-22 at 14:01 +0200, Sylwester Nawrocki wrote:
> > Hi Nicolas,
> >
> > (fixed Simon's email address, apologies for mistyping it, I will make sure
> > it's correct in next iteration)
> >
> > On 22.04.2020 10:53, Nicolas Saenz Julienne wrote:
> > > I've been trying to get this working on my own and got stuck with this
> > > specific
> > > issue. I'm glad you found a solution, it was driving me crazy.
> > >
> > > Out of curiosity how did you found the solution?
> >
> > It took me many days of debugging...given my nearly non existent previous
> > experience in u-boot development.In short, it started with a suggestion to map
> > all memory for CPU as uncached.
> > As in such a case booting was failing I checked where the xhci shared buffer
> > allocation fall and created only a small uncached window to cover those
> > allocations. This was first thing that started working, after fixing the
> > 64-bit pointers setup in XHCI registers.
> > Then I discovered "dcache" command and that was also helpful. It was
> > sufficient
> > to run "dcache off; usb start; dcache on". Then USB worked even after "usb
> > reset"
> > IIRC. But that was with my old development branch based on v2019.10-rc4 tag.
> > Marek tried the same with newer tree and dcache_disable() was not helping,
> > but dcache_flush_all() was.
> >
> > By moving dcache_disable(), dcache_enable() around I found out that it was
> > sufficient to disable dcache before xhci_start() call and to enable it right
> > afterwards.
> >
> > Then I just "bisected" the uncached memory region which narrowed it roughly
> > to the scratchpad buffer allocations. By inspecting the code carefully again
> > it turned there is one more cache flush call needed.
>
> Thanks for the in-depth explanation, it's very much appreciated!

Yes indeed, thank you!


- Simon