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Re: [Xen-devel] [PATCH] V4 pci uart - better cope with UART being temporarily unavailable

On 08/27/2013 04:05 PM, Tomasz Wroblewski wrote:
This happens for example when dom0 disables ioport responses during PCI 
subsystem initialisation. If a __ns16550_poll() happens to be scheduled during 
that time, Xen hangs. Detect and exit that condition.

Amended ns16550_ioport_invalid function to only check IER register, which 
contins 3 reserved (always 0) bits, therefore it's sufficient for that test.

Changes since V3:
* readded invalid port test in the loop in __ns16550, moved it before 
serial_rx_interrupt call

Changes since V2:
* pulled out invalid port test before the loop in __ns16550_poll
* coding style/patch size fixes

Changes since V1:
* added invalid port test in getc()
* changed ns16550_tx_ready to return -EIO and code in serial.[ch] to cope with 
that error condition. If port is temporarily unavailable tx_ready will return 
-EIO and serial driver code will attempt to buffer the character instead of 
dropping it.

Signed-off-by: Tomasz Wroblewski<tomasz.wroblewski@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

since he said:
"(and you may retain the tag if you decide to undo the first of the
two mentioned changes since V2 - I'm fine with it either way)"

V4 undoes that mentioned change, it was wrong.

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