linux-kernel - Re: [PATCH] tty: serial: Use fifo in 8250 console driver

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Date:   Wed, 10 Nov 2021 09:10:14 -0300
From:   Wander Costa <wcosta@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     wander@...hat.com, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Johan Hovold <johan@...nel.org>,
        Andrew Jeffery <andrew@...id.au>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty: serial: Use fifo in 8250 console driver

On Mon, Nov 1, 2021 at 12:33 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Mon, Nov 1, 2021 at 5:22 PM Wander Costa <wcosta@...hat.com> wrote:
> > Em sáb., 30 de out. de 2021 04:41, Andy Shevchenko
> > <andy.shevchenko@...il.com> escreveu:
> > > On Friday, October 29, 2021, <wander@...hat.com> wrote:
>
> ...
>
> > > I don't see any links.
> >
> > Oops, sorry about that. I must have accidentally deleted it while
> > editing the commit message.
> > Here it is https://github.com/walac/serial-console-test.
> > I will update the patch with the link.
>
> Thanks!
>
> ...
>
> > > On how many different UARTs have you tested this? Have you tested oops and NMI contexts?
> > >
> > I only tested in a half dozen machines that I have available. I tried
> > it in panic, warnings, IRQ contexts, etc. Theoretically, this change
> > should not be affected by the context. Theoretically...
> >
> > > What I would like to say here is that the code is being used on zillions of different 8250 implementations here and I would be rather skeptical about enabling the feature for everyone.
> > >
> > I did my homework and studied the 16550 datasheets, but yes, there is
> > always this risk. Maybe people more experienced with PC serial ports
> > than me might think the patch is not worth the risk of breaking some
> > unknown number of devices out there, and I am ok with that. It is a
> > valid point.
>
> Here is a translation of my comment to a roadmap.
>
> 1. Introduce yet another UART quirk or capability (see corresponding
> UART_CAP_* or UART_*_QUIRK definitions)
> 2. Add your patch conditionally based on the above
> 3. Enable it on UART(s) you _have tested_
>
Thank you for the feedback, I submitted a v2 patch with your proposed changes,

Cheers,
Wander

> --
> With Best Regards,
> Andy Shevchenko
>