Re: [Xen-devel] [PATCH v2] xen/arm: initialize vpl011 flag register

[Jeff Kubascik <jeff.kubascik@xxxxxxxxxxxxxxx>]

On 11/25/2019 5:17 PM, Julien Grall wrote:
> Hi,
> 
> On 25/11/2019 20:58, Jeff Kubascik wrote:
>> The tx/rx fifo flags were not set when the vpl011 is initialized. This
>> is a problem for certain guests that are operating in polled mode, as a
>> guest will generally check the rx fifo empty flag to determine if there
>> is data before doing a read. The result is a continuous spam of the
>> message "vpl011: Unexpected IN ring buffer empty" before the first valid
>> character is received. This initializes the flag status register to the
>> default specified in the PL011 technical reference manual.
>>
>> Signed-off-by: Jeff Kubascik <jeff.kubascik@xxxxxxxxxxxxxxx>
> 
> You could have retained my acked-by here :).
> 
> Acked-by: Julien Grall <julien@xxxxxxx>

Apologies, I'm still getting used to submitting patches by mailing list.

> We are in late stage for Xen 4.13 and from what you say this will only
> spam the console (though it is rate-limited). So I don't intend to
> request to be merged in Xen 4.13 (feel free to request it if you think
> it is worth it).
> 
> Instead, I will queue it for the next release in my branch for-next/4.14.

Sounds good!

>>
>> Changes in v2:
>> - Moved uartfr initialization to later point in function after potential
>> return/failure points
> We don't commit the changelog. To help making the committers life
> boring, I would recommend to add --- before it. git am will stripped
> anything after it.
> 
>> ---
> 
> Similar to this one.
> 
>>   xen/arch/arm/vpl011.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
>> index 7bc5eeb207..895f436cc4 100644
>> --- a/xen/arch/arm/vpl011.c
>> +++ b/xen/arch/arm/vpl011.c
>> @@ -668,6 +668,8 @@ int domain_vpl011_init(struct domain *d, struct 
>> vpl011_init_info *info)
>>           goto out2;
>>       }
>>
>> +    vpl011->uartfr = TXFE | RXFE;
>> +
>>       spin_lock_init(&vpl011->lock);
>>
>>       register_mmio_handler(d, &vpl011_mmio_handler,
>>
> 
> --
> Julien Grall
> 

Good to know, I will do this next time.

Thanks,
Jeff Kubascik

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