[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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



On 08/21/2013 12:04 PM, Ian Campbell wrote:
On Tue, 2013-08-13 at 17:12 +0200, Andre Przywara wrote:
The PL011 IMSC register description is somehow fuzzy in the
documentation;

OMG pl011 docs r1p5 issue g says:
         On a read this register returns the current value of the mask on
         the relevant interrupt. On a write of 1 to the particular bit,
         it sets the corresponding mask of that interrupt. A write of 0
         clears the corresponding mask.

Which is perfectly obvious if you read it understanding "mask an
interrupt" in the normal way, but in the introduction to the section on
interrupts it says:

         You can enable or disable the individual interrupts by changing
         the mask bits in the Interrupt Mask Set/Clear Register, UARTIMSC
         on page 3-17. Setting the appropriate mask bit HIGH enables the
         interrupt.

So IMSC is actually the "mask" of the interrupts which are enabled.

What crappy docs!

I agree, I stumbled on this by reading IMSC and wondered how it could be just 0 in the first place, then looking at the Linux code... And honestly I didn't even find the first paragraph, but was wondering why they repeat that "1 sets the mask, 0 clears it" all over the place instead of explicitly stating the meaning for the interrupt ;-)

Regards,
Andre.

  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).

How on earth we got away with this I've idea!

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxxxxx>

Ack + applied, thanks!




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.