[PATCH] serial: 8250: Revert "tty: serial: 8250_core: read only RX if there is something in the FIFO"

Hi Sebastian,

* Sebastian Andrzej Siewior [off-list ref] [150215 09:35]:

This reverts commit 0aa525d11859c1a4d5b78fdc704148e2ae03ae13.

The conditional RX-FIFO read seems to cause spurious interrupts and we
see just:
|serial8250: too much work for irq29

The previous behaviour was "default" for decades and Marvell's 88f6282 SoC
might not be the only that relies on it. Therefore the Omap fix is
reverted for now.

Fixes: 0aa525d11859 ("tty: serial: 8250_core: read only RX if there is
something in the FIFO")
Reported-By: Nicolas Schichan <redacted>
Debuged-By: Peter Hurley [off-list ref]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
* Russell King - ARM Linux | 2015-02-13 23:15:19 [+0000]:

quoted

On Fri, Feb 13, 2015 at 07:51:16PM +0100, Sebastian Andrzej Siewior wrote:

quoted

Something like this maybe?

My personal feeling is that as 0aa525d11859 was wrong, it should be
reverted and this should be another attempt to fix the problem.  In
other words, there should be two patches, one a revert of the previously
known bad commit and this one having another go at it.

I feel that would be a better approach, since then we don't end up
with this change building on a previously know buggy change.  It
would also make the changes to this solution from the previous,
known-to-work-for-decades code more obvious.

Okay. So here is the revert.

After the revert looks like now we get the following on omaps with
8250.. Do you have a fix available somewhere on top of your revert?

Unhandled fault: external abort on non-linefetch (0x1028) at 0xfa06a000
...
[<c04217e8>] (mem_serial_in) from [<c0425480>] (serial8250_do_startup+0xe4/0x694)
[<c0425480>] (serial8250_do_startup) from [<c0427e48>] (omap_8250_startup+0x70/0x144)
[<c0427e48>] (omap_8250_startup) from [<c0425a54>] (serial8250_startup+0x24/0x30)
[<c0425a54>] (serial8250_startup) from [<c04208e4>] (uart_startup.part.14+0x8c/0x1a0)
[<c04208e4>] (uart_startup.part.14) from [<c0420fec>] (uart_open+0xd8/0x134)
[<c0420fec>] (uart_open) from [<c0403e50>] (tty_open+0xdc/0x5e0)
[<c0403e50>] (tty_open) from [<c018f008>] (chrdev_open+0xac/0x188)
...

Regards,

Tony