linux-kernel - Re: [PATCH v14 1/1] tty: serial: Add Nuvoton ma35d1 serial driver support

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Message-Id: <9fecce53-fc7d-4783-9e05-509b1b418589@app.fastmail.com>
Date:   Thu, 15 Jun 2023 18:11:36 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Cc:     "Jacky Huang" <ychuang570808@...il.com>,
        "Rob Herring" <robh+dt@...nel.org>,
        krzysztof.kozlowski+dt@...aro.org, "Lee Jones" <lee@...nel.org>,
        "Michael Turquette" <mturquette@...libre.com>,
        "Stephen Boyd" <sboyd@...nel.org>,
        "Philipp Zabel" <p.zabel@...gutronix.de>,
        "Jiri Slaby" <jirislaby@...nel.org>,
        "Tomer Maimon" <tmaimon77@...il.com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
        soc@...nel.org, schung@...oton.com, mjchen@...oton.com,
        "Jacky Huang" <ychuang3@...oton.com>
Subject: Re: [PATCH v14 1/1] tty: serial: Add Nuvoton ma35d1 serial driver support

On Thu, Jun 15, 2023, at 17:00, Greg Kroah-Hartman wrote:
> On Thu, Jun 15, 2023 at 04:01:55PM +0200, Arnd Bergmann wrote:
>> Since the number is exported to userspace in serial_struct,
>> it might be better to pick a new constant such as
>> 
>> #define PORT_SERIAL_GENERIC (-1)
>> 
>> in order to be less ambiguous. It's a signed integer, so -1
>> would work here this would clearly be a special value, or
>> another option might be to use 255 as something that is
>> slightly less special but still recognizable as something
>> that may have a special meaning.
>
> A new constant would be good, 255 is nice, and then we can move everyone
> to use it unless they can specifically show a reason why it will not
> work for them.
>
> I think originally this was used to do device-specific ioctls, right?
> That shouldn't be happening anymore, hopefully...

The only thing I could find is that you can use TIOCSSERIAL to set
the type between the supported types within a driver, which changes
the behavior in some cases, e.g. the exact size and layout of the
register file or its capabilities.

We may need a proper audit of TIOCSSERIAL anyway, I suspect there
are worse things you can do with other settings.

       Arnd