Re: [Xen-devel] [PATCH] arm/acpi: Add Server Base System Architecture UART support

[Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>]

I'll address your review comments in V2 patch.


On 05/27/2016 09:56 AM, Julien Grall wrote:
> Hello Shanker,
>
> On 27/05/16 15:01, Shanker Donthineni wrote:
>> On 05/27/2016 08:04 AM, Julien Grall wrote:
>>> On 27/05/16 01:28, Shanker Donthineni wrote:
>>>> The ARM Server Base System Architecture describes a generic UART
>>>> interface. It doesn't support clock control registers to set
>>>> baudrate. So, extend the driver probe() to handle SBSA interface
>>>> types and set the baudrate to 115200 for SBSA interfaces.
>>>
>>> I cannot find any mention of the baudrate in the SBSA. Where does it come 
>>> from?
>>>
>> Yes, no where mentioned about the baudrate in SBSA document. I used 115200 
>> based on the  the Linux  PL011 driver.
>
> Looking at the Linux code, it is a default when there is no valid 
> configuration (which may not be suitable for any platform?).
>
> Whilst Linux userspace cares about the baudrate, Xen only use it to configure 
> the hardware. Given that the UART should have been configured by the 
> hardware-specific software, the proper value should be BAUD_AUTO.
>
> If you look at the code, pl011_init_preirq will read the baud rate when 
> uart->baud == BAUD_AUTO but will never be used after.
>
>>> Also the driver is using registers which should not be touch for the SBSA 
>>> UART (see appendix B in the SBSA ARM-DEN-0029 v3.0). So this need to be 
>>> address to get a proper support.
>>>
>> Yes, I agree with you, Which registers it is touching other than baudrate 
>> control registers?
>
> Well, I only gave a quick look and noticed the difference between the SBSA 
> and the pl011 (e.g CR, IFLS,...) . I am sure you can find out the rest of the 
> registers by looking at the code (pl011-uart.h) and the spec.
>
> Regards,
>

-- 
Shanker Donthineni
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux 
Foundation Collaborative Project


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