linux-kernel - Re: [PATCH v5 01/10] pinctrl: generic: Add bi-directional and output-enable

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Date:   Fri, 12 May 2017 14:25:23 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Chris Brandt <Chris.Brandt@...esas.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        jmondi <jacopo@...ndi.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 01/10] pinctrl: generic: Add bi-directional and output-enable

Hi Chris,

On Fri, May 12, 2017 at 2:13 PM, Chris Brandt <Chris.Brandt@...esas.com> wrote:
> On Friday, May 12, 2017, Geert Uytterhoeven wrote:
>> Jacopo, Chris: Would two bits per pin/function (none, input, output,
>> bidir)
>> be sufficient?
>> That makes one u16 per pin. So roughtly 12 ports x 16 pins => 384 bytes.
>> Plus code to handle it. After all not that bad...
>
> OK...I give up!
> If that's what it takes to get it, I'm fine.
>
> NOTE, your math is a little off, the issue is that depending on the
> function that you use, you might need to do extra settings, so you'd
> have to have a lookup table for every pin & function.
> Each pin can have 1 of 8 functions (which is good because a 'byte' has
> 8 bits).
>
> So,
>  12 ports x 16 pins => 384 bytes  (this table would just be for checking if bi-dir is needed)
>  12 ports x 16 pins => 384 bytes  (this table would just be for checking if input is needed)
>  12 ports x 16 pins => 384 bytes  (this table would just be for checking if input is needed)
         ------------
>                      1,152 bytes

12 x 16 = 192, not 384.

Do you need all possible combinations of input, output, and bi-dir?
I assumed they're mutually exclusive. If not, you need 3 bits/pin/function.

> But then...there are package variations so you need another entire
> table for those parts.
>    1,152 bytes x 2 = 2,304 bytes

With packages, do you mean e.g. RZ/A1H vs. RZ/A1L? These indeed differ, but
should use different compatible values.
Or do you mean QFP/BGA256 vs. BGA324? Isn't the former a subset of the latter?

> #What we should really do is just make a look-up table (tables) for the
> 'special' ones. But, we can have that discussion in a different thread.

Yep, depending on what gives the smallest code/data size.

> There is still a need for "input-enable" and "output-enable" for the timer
> pins. Because, when you choose the pin to be connected to the MTU2 timer,
> the pin can be used as either input-capture/output-compare/PWM and that's
> the user's choice. So that's probably a valid usage of the generic pin
> properties for configuration.

OK.

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