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

[Nicolas Saenz Julienne]

On Wed, 2020-04-22 at 11:26 +0200, Nicolas Saenz Julienne wrote:
> On Wed, 2020-04-22 at 17:21 +0800, Bin Meng wrote:
> > Hi Nicolas,
> > 
> > On Wed, Apr 22, 2020 at 4:53 PM Nicolas Saenz Julienne
> > <nsaenzjulienne at suse.de> wrote:
> > > Hi Sylwester, Marek
> > > 
> > > On Tue, 2020-04-21 at 18:50 +0200, Sylwester Nawrocki wrote:
> > > > In current code there is no cache flush after initializing the
> > > > scratchpad
> > > > buffer array with the scratchpad buffer pointers. This leads to a
> > > > failure
> > > > of the "slot enable" command on the rpi4 board (Broadcom STB PCIe
> > > > controller + VL805 USB hub) - the very first TRB transfer on the command
> > > > ring fails and there is a timeout while waiting for the command
> > > > completion
> > > > event. After adding the missing cache flush everything seems to be
> > > > working
> > > > as expected.
> > > > 
> > > > Signed-off-by: Sylwester Nawrocki <s.nawrocki at samsung.com>
> > > > Reviewed-by: Bin Meng <bmeng.cn at gmail.com>
> > > > ---
> > > 
> > > 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?
> > > 
> > > >  drivers/usb/host/xhci-mem.c | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > > > 
> > > > diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> > > > index 93450ee..729bdc3 100644
> > > > --- a/drivers/usb/host/xhci-mem.c
> > > > +++ b/drivers/usb/host/xhci-mem.c
> > > > @@ -393,6 +393,9 @@ static int xhci_scratchpad_alloc(struct xhci_ctrl
> > > > *ctrl)
> > > >               scratchpad->sp_array[i] = cpu_to_le64(ptr);
> > > >       }
> > > > 
> > > > +     xhci_flush_cache((uintptr_t)scratchpad->sp_array,
> > > > +                      sizeof(u64) * num_sp);
> > > > +
> > > 
> > > Marek, souldn't running 'dcache off; icache off' be equivalent to this
> > > (which
> > > didn't do the trick for me)? or am I missing somthing?
> > 
> > I guess something is wrong with RPi4's "dcache off" command ..
> 
> You can't trust anything these times :)
> 
> I'll look into it.

Well it's not only that disabling the caches was needed, but also avoiding
64bit accesses, since I was missed that one, I didn't see the change in
behavior. In other words, dcache/icache commands are fine.

Sorry for the noise.

Regards,
Nicolas

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