Re: [Xen-devel] [PATCH 26/27 v8] xen/arm: vpl011: Correct the logic for asserting/de-asserting SBSA UART TX interrupt

[Julien Grall <julien.grall@xxxxxxx>]

Hi Bhupinder,

I am just commenting on the commit message, Andre already commented the 
code.
On 28/08/17 09:56, Bhupinder Thakur wrote:
> This patch fixes the issue observed when pl011 patches were tested on
> the junos hardware by Andre/Julien. It was observed that when large output is
> generated such as on running 'find /', output was getting truncated 
> intermittently
> due to OUT ring buffer getting full.
>
> This issue was due to the fact that the SBSA UART driver expects that when
> a TX interrupt is asserted then the FIFO queue should be atleast half empty and
> that it can write N bytes in the FIFO, where N is half the FIFO queue size, 
> without
> the bytes getting dropped due to FIFO getting full.
>
> This requirement is as per section 3.4.2 of [1], which is:
>
> -------------------------------------------------------------------------------
> UARTTXINTR
This register does not exist in the SBSA, so you cannot say it is a 
requirement from the specification. The emulation should be based on the 
specification and not how a driver behave. You don't know how other OS 
have implemented the driver.
As I mentioned in my previous answer, we are in process to clarify in 
the specification and we can currently assume the interrupt will be 
triggered at halfway.
So the commit message should reflect that.

Cheers,

--
Julien Grall

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