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Re: [Xen-devel] [PATCH] PL011: fix reverse logic for interrupt mask register

On 08/22/2013 08:23 AM, Ian Campbell wrote:
> On Wed, 2013-08-21 at 17:11 +0100, Julien Grall wrote:
>> On 08/13/2013 04:12 PM, Andre Przywara wrote:
>>> The PL011 IMSC register description is somehow fuzzy in the
>>> documentation; by comparing it with the Linux implementation one can
>>> see that the logic is actually reversed to Xen's implementation:
>>> A "0" in field means interrupt disabled, a "1" enables it.
>>> Therefore we enabled all interrupts instead of disabling them in the
>>> beginning and later on masked the wrong interrupts.
>>> Unclear how this worked on the Versatile Express, but this fix is
>>> needed to get Calxeda Midway running (and works on VExpress, too).
>> On my Versatile Express, the keyboard is unusable with this patch.
>> Xen receives random keys and sometimes nothing is printed on the serial
>> port.
>> By reverting this patch on my tree, I'm able to use correctly the serial
>> port.
> :-/ Andre did say this patch worked on vexpress for him.
> I'm pretty certain Andre's patch is correct in its own right. But the
> fact that it worked before does seem to imply that there are other
> issues with the pl011 driver, it's likely that this change has just
> exposed a latent one.
> Could this be related somehow to the baud rate setting change? I
> wouldn't have expected so but "random keys" and nothingness could be a
> symptom of incorrect baud too.
> Does anyone have time to look into this?

If RTI interrupt are enabled (see small patch below), the UART works perfectly
on the versatile express.

The PL011 documentation says the bit is used to mask/unmask receive interrupt
timeout. I don't understand why this interrupt is useful and the documentation
doesn't help me...

diff --git a/xen/drivers/char/pl011.c b/xen/drivers/char/pl011.c
index 0e1eb64..e4bd702 100644
--- a/xen/drivers/char/pl011.c
+++ b/xen/drivers/char/pl011.c
@@ -140,7 +140,7 @@ static void __init pl011_init_postirq(struct serial_port 
     pl011_write(uart, ICR, OEI|BEI|PEI|FEI);
     /* Unmask interrupts */
-    pl011_write(uart, IMSC, OEI|BEI|PEI|FEI|TXI|RXI);
+    pl011_write(uart, IMSC, RTI|OEI|BEI|PEI|FEI|TXI|RXI);
 static void pl011_suspend(struct serial_port *port)

Julien Grall

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