linux-kernel - Re: [PATCH] serial: 8250: add option to disable registration of legacy ISA ports

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Date:   Sun, 31 Jan 2021 19:47:11 +0000
From:   Måns Rullgård <mans@...sr.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] serial: 8250: add option to disable registration of
 legacy ISA ports

Andy Shevchenko <andy.shevchenko@...il.com> writes:

> On Thursday, January 28, 2021, Mans Rullgard <mans@...sr.com> wrote:
>
>> On systems that do not have the traditional PC ISA serial ports, the
>> 8250 driver still creates non-functional device nodes.  This change
>> makes only ports that actually exist (PCI, DT, ...) get device nodes.
>>
>>
>
> This is kinda ABI breakage. At least this will break x86 platforms with
> HSUARTs (all modern ones) that are used in embedded systems.
>
> I think you would rather need an option to disable this and select it by
> the platforms where it is known not to break anything.

What exactly breaks?  The new option is enabled by default, just like
the one right beside it (SERIAL_8250_PNP), so nothing at all changes
unless this is actively disabled.  On a system that doesn't have those
ports, any attempt to access the device nodes produces some kind of
error.  How is it breaking anything to not create device nodes for
hardware that doesn't exist?

-- 
Måns Rullgård