On Wed, Mar 18, 2015 at 01:02:47AM +0100, Jakub Kicinski wrote:

From: Jakub Kicinski <redacted>

Since pre-git era PL011 used an elaborate scheme to load data
to TX FIFO.  Only TX IRQ handler was loading data into the FIFO,
which required the IRQ to fire before any transmission started
(to load the first batch of characters).  Initial IRQ was fired
by putting UART into loopback mode and writing an arbitrary
character during .startup().

Unfortunately some PL011-compatible UART (most notably BCM2708
in Raspberry Pi) would transmit the arbitrary character even
though the device was in loopback mode.  Commit 734745caeb9f
("serial/amba-pl011: Activate TX IRQ passively") solved this
issue by loading the first batch explicitly from .start_tx()
handler.  It employed quite a complex scheme involving IRQ
counting and a delayed work.

f2ee6dfa0e85 ("serial/amba-pl011: Leave the TX IRQ alone when
the UART is not open") was an attempt to optimise the loading
by assuming that when the device is opened second time TX IRQ
from the previous transmission will still be pending.  This
assumption is incorrect if the device is closed with FIFO full
because FIFO will be programmatically flushed and therefore no
IRQ will be pending on next .open().

This patch simplifies the code and fixes above problem. It should
also make things a bit more efficient as the FIFO was not filled
properly after the driver seen more than two IRQs.

Fixes: f2ee6dfa0e85 ("serial/amba-pl011: Leave the TX IRQ alone when the UART is not open")
Signed-off-by: Jakub Kicinski <redacted>
---
v2:
 - don't try to load FIFO from outside of IRQ handler
   if IRQ is unmasked (change to pl011_start_tx_pio());
 - don't check for FIFO_FULL at the end of load from IRQ;
 - remove unnecessary newlines.
---
 drivers/tty/serial/amba-pl011.c | 113 +++++++++++++---------------------------
 1 file changed, 35 insertions(+), 78 deletions(-)

As I think this does much the same thing Dave Martin's patch does, I
want him to ack this before I can accept it.

thanks,

greg k-h