linux-kernel - [PATCH RT 0/2] serial: 8250: atomic console fixups

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Date:   Fri, 10 Jan 2020 16:45:30 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Dick Hollenbeck <dick@...tplc.com>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: [PATCH RT 0/2] serial: 8250: atomic console fixups

Dick Hollenbeck pointed out[0] that serial usage for non-consoles
was dramatically affected due to the atomic console
implementation. Indeed, the implementation was taking the global
console_atomic_lock for _all_ 8250 ports, regardless if they were
consoles or not.

This series fixes that by only using the cpu-lock if the port is
a console. While making those changes, I realized that the clear
counter/ier-cache is not needed, so that is also removed.

Dick also pointed out that the IER accessor functions were using
non-typical names. These are updated and moved to inline macros.

Finally, I noticed that the fsl, ingenic, and mtk variants were
directly accessing IER. These are now also appropriately wrapped.

In his suggestion, Dick did optimizations regarding IER caching.
However, these are _not_ included because they may have some
unwanted side-effects. For example, I noticed a few places in
8250 code where the value of uart_8250_port->ier is expected to
be different than the hardware register.

John Ogness

[0] https://www.spinics.net/lists/linux-rt-users/msg21480.html

John Ogness (2):
  serial: 8250: only atomic lock for console
  serial: 8250: fsl/ingenic/mtk: fix atomic console

 drivers/tty/serial/8250/8250.h         | 65 ++++++++++++++-------
 drivers/tty/serial/8250/8250_core.c    |  6 +-
 drivers/tty/serial/8250/8250_dma.c     |  4 +-
 drivers/tty/serial/8250/8250_fsl.c     |  9 +++
 drivers/tty/serial/8250/8250_ingenic.c |  7 +++
 drivers/tty/serial/8250/8250_mtk.c     | 29 ++++++++-
 drivers/tty/serial/8250/8250_port.c    | 81 ++++++--------------------
 7 files changed, 109 insertions(+), 92 deletions(-)

-- 
2.20.1