linux-kernel - Re: [PATCH v4 2/5] serial/8250: Use the cache value of the FCR register

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Message-ID: <CAAq0SU==UJpdTN2YNm_2KNGQmSKMOU97fFb-wTV2VM=vO5pPCw@mail.gmail.com>
Date:   Thu, 17 Mar 2022 09:03:55 -0300
From:   Wander Costa <wcosta@...hat.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Wander Lairson Costa <wander@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Serge Semin <fancer.lancer@...il.com>,
        Lukas Wunner <lukas@...ner.de>,
        Pali Rohár <pali@...nel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        André Goddard Rosa <andre.goddard@...il.com>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Jon Hunter <jonathanh@...dia.com>, phil@...pberrypi.com
Subject: Re: [PATCH v4 2/5] serial/8250: Use the cache value of the FCR register

On Thu, Mar 17, 2022 at 5:31 AM Ilpo Järvinen
<ilpo.jarvinen@...ux.intel.com> wrote:
>
> On Wed, 16 Mar 2022, Wander Lairson Costa wrote:
>
> > commit 5021d709b31b ("tty: serial: Use fifo in 8250 console driver")
> > erroneous tries to read the FCR register content, but this register is
> > write-only.
> >
> > This patch fixes that by reading the content from the port struct fcr
> > field.
> >
> > Thanks to Jon Hunter and Jiri Slaby.
> >
> > Suggested-by: Jiri Slaby <jirislaby@...nel.org>
> > Reported-by: Jon Hunter <jonathanh@...dia.com>
> > Signed-off-by: Wander Lairson Costa <wander@...hat.com>
> > ---
> >  drivers/tty/serial/8250/8250_port.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> > index 2abb3de11a48..9f3fa9fe2a4e 100644
> > --- a/drivers/tty/serial/8250/8250_port.c
> > +++ b/drivers/tty/serial/8250/8250_port.c
> > @@ -3410,7 +3410,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
> >
> >       use_fifo = (up->capabilities & UART_CAP_FIFO) &&
> >               port->fifosize > 1 &&
> > -             (serial_port_in(port, UART_FCR) & UART_FCR_ENABLE_FIFO) &&
> > +             (up->fcr & UART_FCR_ENABLE_FIFO) &&
>
> Didn't you just add this line in 1/5? Please merge this kind of fixes that
> are due to development history of a change to the main patch itself.
>

The reason is that 1/5 has been applied in 5.17 and then reverted, so
I thought it would make it easier for reviewers if I sent the new
fixes in different commits. If that's not the case, I can send a
squashed version with the changelog described in 0/5.