Re: Troubles running Xen on Raspberry Pi 4 with 5.6.1 DomU

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 13 May 2020, Julien Grall wrote:
> Hi,
> 
> On 13/05/2020 01:33, Stefano Stabellini wrote:
> > I worked with Roman to do several more tests and here is an update on
> > the situation. We don't know why my patch didn't work when Boris' patch
> > [1] worked.  Both of them should have worked the same way.
> > 
> > Anyway, we continued with Boris patch to debug the new mmc error which
> > looks like this:
> > 
> > [    3.084464] mmc0: unrecognised SCR structure version 15
> > [    3.089176] mmc0: error -22 whilst initialising SD card
> > 
> > I asked to add a lot of trancing, see attached diff.
> 
> Please avoid attachment on mailing list and use pastebin for diff.
> 
> > We discovered a bug
> > in xen_swiotlb_init: if io_tlb_start != 0 at the beginning of
> > xen_swiotlb_init, start_dma_addr is not set correctly. This oneline
> > patch fixes it:
> > 
> > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> > index 0a40ac332a4c..b75c43356eba 100644
> > --- a/drivers/xen/swiotlb-xen.c
> > +++ b/drivers/xen/swiotlb-xen.c
> > @@ -191,6 +191,7 @@ int __ref xen_swiotlb_init(int verbose, bool early)
> >           * IO TLB memory already allocated. Just use it.
> >           */
> >          if (io_tlb_start != 0) {
> > +               start_dma_addr = io_tlb_start;
> >                  xen_io_tlb_start = phys_to_virt(io_tlb_start);
> >                  goto end;
> >          }
> > 
> > Unfortunately it doesn't solve the mmc0 error.
> > 
> > 
> > As you might notice from the logs, none of the other interesting printks
> > printed anything, which seems to mean that the memory allocated by
> > xen_swiotlb_alloc_coherent and mapped by xen_swiotlb_map_page should be
> > just fine.
> > 
> > I am starting to be out of ideas. Do you guys have any suggestions on
> > what could be the issue or what could be done to discover it?
> 
> Sorry if my suggestions are going to be obvious, but I can't confirm whether
> this was already done:
>     1) Does the kernel boot on baremetal (i.e without Xen)? This should help
> to confirm whether the bug is Xen is related.

Yes it boots

>     2) Swiotlb should not be necessary for basic dom0 boot on Arm. Did you try
> to disable it? This should help to confirm whether swiotlb is the problem or
> not.

It boots disabling swiotlb-xen


>     3) Did you track down how the MMC read the SCR structure?
 
Not yet