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

[Ayan Kumar Halder <ayankuma@amd.com>]

On 02/12/2024 20:53, Julien Grall wrote:
> Hi Ayan,
Hi Julien,
>
> 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?
https://developer.arm.com/documentation/102670/0101 - Cortex-R82 
processor TRM
>
>> 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. 
Actually I was quoting from Cortex-R82 TRM.
> The code you modify below is 64-bit so Armv8 only.
>
> The code itself LGTM.

Ack.

- Ayan

>
> Cheers,
>