Re: [Qemu-devel] [PATCH v2 4/4] pl011: re-evaluate rx interrupt when fifo trigger changes

[Peter Maydell]

On 16 March 2014 15:57, Peter Maydell <address@hidden> wrote:
> On 14 March 2014 18:22, Rob Herring <address@hidden> wrote:
>> From: Rob Herring <address@hidden>
>>
>> When setting the fifo trigger level, the rx interrupt needs to be asserted
>> if the current fifo level matches. This is more for correctness as the
>> level is currently never changed.
>>
>> Signed-off-by: Rob Herring <address@hidden>
>> ---
>>  hw/char/pl011.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/hw/char/pl011.c b/hw/char/pl011.c
>> index 5e664f4..3903933 100644
>> --- a/hw/char/pl011.c
>> +++ b/hw/char/pl011.c
>> @@ -131,6 +131,10 @@ static void pl011_set_read_trigger(PL011State *s)
>>      else
>>  #endif
>>          s->read_trigger = 1;
>> +
>> +    if (s->read_count == s->read_trigger) {
>> +        s->int_level |= PL011_INT_RX;
>> +    }
>
>>=, surely?

On closer inspection of the TRM it's not quite that simple (section 2.8.2).
We need to assert the interrupt only if the change in the read_trigger
means the FIFO is now above the new threshold but wasn't above
the old one, and only if the FIFOs are enabled -- if the FIFO is disabled
the threshold doesn't figure into the interrupt level.

thanks
-- PMM