linux-kernel - Re: [PATCH 0/2] Move uart_register_driver call to device probe for pl010 and sh-sci

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Date:   Sun, 26 Mar 2017 11:22:57 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Sjoerd Simons <sjoerd.simons@...labora.co.uk>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>
Subject: Re: [PATCH 0/2] Move uart_register_driver call to device probe for
 pl010 and sh-sci

Hi Russell, Sjoerd,

On Fri, Mar 24, 2017 at 5:42 PM, Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> On Fri, Mar 24, 2017 at 05:26:32PM +0100, Sjoerd Simons wrote:
>> When testing on a Renesas board with the PL010 serial driver enabled
>> serial output broke. Turns out the minor device numbers for both
>> drivers happen to overlap, causing whichever driver happened to be the
>> second one to register to fail.
>
> How the **** has the SH serial driver ended up with overlapping device
> numbers?

Interesting...

> What happened to our maintained list of allocated major/minor device
> numbers, which is supposed to stop crap like this happening?

AMBA PL010 has been assigned major 204, minors 16..31,
SCI has been assigned major 204, minors 8..11.

Over the years, Renesas SoCs have been gaining more and more serial
ports, leading to

    #define SCI_NPORTS CONFIG_SERIAL_SH_SCI_NR_UARTS

with CONFIG_SERIAL_SH_SCI_NR_UARTS=20 in shmobile_defconfig and
multi_v7_defconfig (although the maximum value on any supported SoC is 18).

But once the value becomes 5 or more, it starts overflowing into the ttyFWx
and ttyAMx space.

How to solve this?
Time for the serial subsystem to switch to dynamic minors, and get rid of the
what-is-your-serial-port-called-again-on-this-platform
multi-million-euro question?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds