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

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Date:   Fri, 12 May 2017 12:13:41 +0000
From:   Chris Brandt <Chris.Brandt@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Walleij <linus.walleij@...aro.org>
CC:     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 Geert and Linus,

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

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

However, if these tables are constants, they will reside in flash for the
XIP_KERNEL systems, so that's OK.

#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.

One final note:

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.

Sorry Jacopo, but we'll need another round of patches.
It sounds like for sure the bi-direction needs to get ripped back out.

Chris