Re: [PATCH v2 1/2] xen/mpu: Map early uart when earlyprintk on

[Julien Grall <julien@xxxxxxx>]

Hi Ayan,

On 27/11/2024 18:39, Ayan Kumar Halder wrote:
> CONFIG_EARLY_UART_SIZE is introduced to let user provide physical size of
> early UART. Unlike MMU where we map a page in the virtual address space,
> here we need to know the exact physical size to be mapped.
> As VA == PA in case of MPU, the memory layout follows exactly the hardware
> configuration. As a consequence, we set  EARLY_UART_VIRTUAL_ADDRESS as physical
> address.
>
> EARLY_UART_BASE_ADDRESS and EARLY_UART_SIZE should be aligned to the minimum
> size of MPU region (ie 64 bits) as per the hardware restrictions. Refer ARM
> DDI 0600A.d ID120821 A1.3 "A minimum protection region size of 64 bytes.".
>
> UART is mapped as nGnRE region (as specified by ATTR=100 , refer G1.3.13,
> MAIR_EL2, "---0100 Device memory nGnRE") and Doc ID - 102670_0101_02_en
I can't find the Doc you point online. Do you have a link?

> Table 4-3, Armv8 architecture memory types (nGnRE - Corresponds to Device in
> Armv7 architecture). Also, it is mapped as outer shareable, RW at EL2 only
I don't quite understand why you mention Armv7 here. The code you modify 
below is 64-bit so Armv8 only.
The code itself LGTM.

Cheers,

--
Julien Grall