linux-kernel - Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands

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Message-ID: <CANiq72=7SX3vrC0uY2uoFcZ7C0Zdfn-eOPuLpdb-dKA4=mLJuQ@mail.gmail.com>
Date:   Tue, 27 Feb 2018 20:31:44 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Willy Tarreau <w@....eu>
Cc:     Robert Abel <rabel@...ertabel.eu>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands

On Tue, Feb 27, 2018 at 6:19 AM, Willy Tarreau <w@....eu> wrote:
> On Mon, Feb 26, 2018 at 11:43:36PM +0100, Robert Abel wrote:
>> On 26 Feb 2018 17:49, Miguel Ojeda wrote:
>> > On a general note, the code seems a bit convoluted for what it does,
>> > specially without the comment written in the commit message :-) Isn't
>> > it simpler to use a tiny array in the stack and put the numbers to be
>> > converted instead of modifying the input sequence and dancing with
>> > pointers?
>>
>> That's what I felt at first, too. If we can drop the backwards
>> compatibility of repeated xy commands, the whole affair gets much
>> easier, but will unfortunately break existing use.
>>
>> Ex. ^[[Lx004y002x006; --> x6y2, because repeats of x would just
>> overwrite earlier values. That's what the while loop allowed in the
>> first place.
>>
>> I suspect the while loop to parse was just a clever way of parsing y
>> followed by x and x followed by y using the same code and the
>> overwriting behavior is actually an unaccounted-for side-effect.
>
> Well actually I don't see a problem there at all. The principle is simply
> to accept any sequence assigning x or y or both. If you write x4y2x6, it
> simply means that you changed your mind regarding x and that the last
> value (6) is the one you want. Just as if you wrote "^[[Lx4;^[[y2;^[[x6;".
> The while loop doesn't even try to do anything clever, it simply parses
> everything matching x and y followed by digits. I think the only reason
> for having both x and y processed in the same loop was to call
> charlcd_gotoxy() only once for both axes.
>

Robert, Willy, Geert, Andy: what about this? (sending the patch
separately, otherwise gmail messes the code up).

Cheers,
Miguel

> Regards,
> Willy