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[v5,0/1] serial/8250: Use fifo in 8250 console driver

Message ID 20220331190257.101781-1-wander@redhat.com
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Series serial/8250: Use fifo in 8250 console driver | expand

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Wander Lairson Costa March 31, 2022, 7:02 p.m. UTC 
This is v5 of the serial fifo patch. In relation to the previous
reverted patch, I describe the main changes in the "What changed from
v3" section.

What changed from v4
--------------------

* It squashes all the patches in a single patch
* It adds `port-state &&` check in the `use_fifo` condition as a
* preventive measure.

What changed from v3
--------------------

* Reads the FCR value from the port struct. The earlier patch
erroneously read the value from the controller, but FCR is a write-only
register. Thanks to Jiri Slaby for point this out.

* Use tx_loadsz as the transmitter fifo size. We previously used the
port->fifosize field, which caused data loss in some controllers. Thanks
Jon Hunter for the bug report.

* Exclude the BCM283x from fifo write. This is based on Phil Elwell's
original patch [1].

* Check if the port is initialized before write through fifo.
The serial driver set the value of uart_8250_port.fcr in the function
serial8250_config_port, but only writes the value to the controller
register later in the initalization code. That opens a small window in
which is not safe to use the fifo for console write. Unfortunately, I
lost track of who originally reported the issue. If s/he is reading
this, please speak up so I can give you the due credit.

[1] https://lore.kernel.org/all/20220126141124.4086065-1-phil@raspberrypi.com/

Wander Lairson Costa (1):
  serial/8250: Use fifo in 8250 console driver

 drivers/tty/serial/8250/8250_port.c | 68 ++++++++++++++++++++++++++---
 1 file changed, 62 insertions(+), 6 deletions(-)