linux-kernel - Re: [PATCH] serial: 8250: probe all 16550A variants by default

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Message-ID: <20200525204827.GC445190@localhost>
Date:   Mon, 25 May 2020 13:48:27 -0700
From:   Josh Triplett <josh@...htriplett.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-serial@...r.kernel.org, jslaby@...e.com,
        andriy.shevchenko@...ux.intel.com, lukas@...ner.de,
        heikki.krogerus@...ux.intel.com, vigneshr@...com,
        lkml <linux-kernel@...r.kernel.org>, fido_max@...ox.ru,
        radu-andrei.bulie@....com
Subject: Re: [PATCH] serial: 8250: probe all 16550A variants by default

On Mon, May 25, 2020 at 09:52:54PM +0300, Vladimir Oltean wrote:
> Hi Josh,
> 
> On Mon, 25 May 2020 at 20:28, Josh Triplett <josh@...htriplett.org> wrote:
> >
> > On Mon, May 25, 2020 at 04:02:38PM +0300, Vladimir Oltean wrote:
> > > On NXP T1040, the UART is typically detected as 16550A_FSL64. After said
> > > patch, it gets detected as plain 16550A and the Linux console is
> > > completely garbled and missing characters.
> >
> > Interesting that there's *new* powerpc hardware that needs these
> > variants. I based the patch on the fact that, on x86 at least, hardware
> > using these variants hasn't been made for a long time.
> >
> > In the hopes of preserving at least part of the benefit of the patch,
> > could you please change it to `default y if !X86_64`?
> >
> 
> Why don't you add CONFIG_SERIAL_8250_16550A_VARIANTS=n in x86_64_defconfig?

In general, it seems preferable to me when the defconfig files differ
less from the defaults encoded in Kconfig.

You're proposing a change to the default; could you please include one
or the other additional change in your patch to preserve the behavior on
x86_64?

> > >  drivers/tty/serial/8250/Kconfig | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
> > > index af0688156dd0..89c7ecb55619 100644
> > > --- a/drivers/tty/serial/8250/Kconfig
> > > +++ b/drivers/tty/serial/8250/Kconfig
> > > @@ -63,6 +63,7 @@ config SERIAL_8250_PNP
> > >  config SERIAL_8250_16550A_VARIANTS
> > >       bool "Support for variants of the 16550A serial port"
> > >       depends on SERIAL_8250
> > > +     default y
> > >       help
> > >         The 8250 driver can probe for many variants of the venerable 16550A
> > >         serial port. Doing so takes additional time at boot.
> > > --
> > > 2.25.1
> > >
> 
> Thanks,
> -Vladimir