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

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.


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