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Re: [PATCH 10/12] xen/arm: if is_domain_direct_mapped use native UART address for vPL011

On 01/05/2020 02:26, Stefano Stabellini wrote:
On Wed, 15 Apr 2020, Julien Grall wrote:
Hi Stefano,

On 15/04/2020 02:02, Stefano Stabellini wrote:
We always use a fix address to map the vPL011 to domains. The address
could be a problem for domains that are directly mapped.

Instead, for domains that are directly mapped, reuse the address of the
physical UART on the platform to avoid potential clashes.

How do you know the physical UART MMIO region is big enough to fit the PL011?

That cannot be because the vPL011 MMIO size is 1 page, which is the
minimum right?

No, there are platforms out with multiple UARTs in the same page (see sunxi for instance).

What if the user want to assign the physical UART to the domain + the vpl011?

A user can assign a UART to the domain, but it cannot assign the UART
used by Xen (DTUART), which is the one we are using here to get the
physical information.

(If there is no UART used by Xen then we'll fall back to the virtual
addresses. If they conflict we return error and let the user fix the

If there is no UART in Xen, how the user will know the addresses conflicted? Earlyprintk?


Julien Grall



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