linux-kernel - Re: [RFT PATCH 5/7] gpio: exar: unduplicate address and offset computation

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Date:   Mon, 2 Nov 2020 11:16:51 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [RFT PATCH 5/7] gpio: exar: unduplicate address and offset computation

On Mon, Oct 26, 2020 at 3:51 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Mon, Oct 26, 2020 at 4:23 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> >
> > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> >
> > Provide and use helpers for calculating the register address and bit
> > offset instead of hand coding it in every function.
>
> Can you check code generation on x86, for example?
>
> Sometimes compilers are eager to use idiv assembly instruction which
> does simultaneously / and %.
> I dunno if a) it's used for / 8 and % 8 since 8 is 2^3, b) splitting
> to functions makes the above optimisation impossible.
>

Is this optimization really needed though? It's not like it's a hot
path if it's protected by a mutex anyway. I prefer cleaner code here.

Bartosz