Re: [PATCH 7/7] xen/arm: Blacklist some sun7i UARTs

[Ian Campbell <Ian.Campbell@citrix.com>]

On Sat, 2013-09-21 at 21:28 +0100, Julien Grall wrote:
> On 09/20/2013 10:41 PM, Ian Campbell wrote:
> > On Fri, 2013-09-20 at 20:02 +0100, Julien Grall wrote:
> >
> >>> +    /*
> >>> +     * These UARTs share a page with the Xen console UART, so we don't
> >>> +     * want to map them through.
> >>> +     */
> >>> +    DT_MATCH_PATH("/soc@01c00000/serial@01c28000"),
> >>> +    DT_MATCH_PATH("/soc@01c00000/serial@01c28400"),
> >>> +    DT_MATCH_PATH("/soc@01c00000/serial@01c28800"),
> >>> +    DT_MATCH_PATH("/soc@01c00000/serial@01c28c00"),
> >>
> >> Can we blacklist all the UARTs via a DT_MATCH_COMPATIBLE? It's better
> >> than relying on the path that can be changed easily in the device tree.
> >
> > There are other UARTS (at 0x1c29xxx) which could safely be exposed to
> > dom0. Perhaps it is better to just blacklist the whole lot though.
> 
> These UARTs also share the same page, what prevents the user to use 
> these UARTs?

Nothing, but because they don't share a page with the xen UART they
don't cause it to get exposed to dom0.

> I have noticed that all the UARTs, except UART0, have a property : 
> status = "disabled". So Xen won't map the UART in dom0 memory.

That bit is new since I initially wrote this patch.

> > Ultimately this is just a hack for the fact that Xen is not currently
> > smart enough to figure out which devices conflict in this way...
> 
> After my comment above, do we really need to blacklist all the other 
> UARTs? As we only support the cubieboard 2, if we only want a hack, I 
> think we can safely avoid this patch for now.

There are quite a few Allwinner A20 based devices out there, e.g. I've
got a MELE M5 which I ultimately hope will work too, so I'd be reluctant
to hardcode cubie specifics.

Probably just blacklisting all the UARTs is the easiest way to go for
now -- typically only one of them is usefully exposed on the systems
I've seen anyway and most of the others are pin muxed with something
more useful, like an MMC device.

Ian.