Re: [Xen-devel] [PATCH 0/2] Raspberry Pi 4 support

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

Thank you for your series. Please use git-send-email so your series is threaded 
correctly and sent in plain text (not HTML!).
On 24/07/2019 15:34, Stewart Hildebrand wrote:
> This is a series to enable printk and UART console for Raspberry Pi 4.
>
> I have been able to get Xen+dom0+domUs booting. Tested with Xen 4.12 and Linux 
> 4.19.y (Raspberry Pi linux tree + a couple of patches). Please see [1] for build 
> instructions and limitations.
I guess you are not using Andre's ATF port? If you are, then Xen 4.12 is 
definitely not safe on that platform because we don't handle reserved-region yet 
and therefore Xen may re-use some of those regions.
Also, there a few other interesting problems with the RPI4 that will need to be 
solved:
   1) The UART is sharing the same page as some other devices. We either need 
to blacklist them so they can't be used by a guest (including Dom0), or we need 
to trap and sanitize access.
   2) Xen is mapping memory using 1GB mapping. AFAIK, there are 1GB slot that 
is shared between RAM and MMIO. This will result to cache incoherency.
> Andre – it appears that we each independently came up with a printk 
> configuration [2]. With this series, you’d no longer need to remember the base 
> address, just do CONFIG_EARLY_PRINTK=rpi4.
Please no more earlyprintk alias. There are no real value for them other than 
cluttering a bit more Rules.mk.
This platform will definitely need some documentation as support is still WIP. 
So the earlyprintk configuration can be written in the wiki page.
Cheers,

--
Julien Grall

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