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

[Nicolas Saenz Julienne]

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!

Regards,
Nicolas

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