Message-ID: <20170119172959.pyulsvak4wpqor2x@lukather>
Date:   Thu, 19 Jan 2017 18:29:59 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Icenowy Zheng <icenowy@...c.xyz>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Andre Przywara <andre.przywara@....com>,
        ext Tony Lindgren <tony@...mide.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] [PATCH 1/2] drivers: pinctrl: add driver for
 Allwinner H5 SoC

On Thu, Jan 19, 2017 at 09:11:49PM +0800, Icenowy Zheng wrote:
> 19.01.2017, 17:23, "Linus Walleij" <linus.walleij@...aro.org>:
> > On Wed, Jan 18, 2017 at 10:44 AM, Andre Przywara <andre.przywara@....com> wrote:
> >
> >>  Any future SoCs could then just use that compatible and would describe
> >>  the SoC details in the DT, like it's meant to be and like we do already,
> >>  but extended by putting the mux value in there as well.
> >>  So the only kernel contribution would then be the DT, really, (...)
> >
> > Your different positions have existed since the inception of the
> > pinctrl subsystem:
> >
> > - One camp (myself included) wanted to describe the hardware mostly
> >   in the driver: functions, groups etc are tables in the driver file.
> >
> > - Another camp (OMAP included) think that the device tree should take
> >   store most things: groups functions, etc.
> >
> > What we know for sure should be described in DT is how different
> > IP blocks are connected in an SoC (e.g. interrupts, clocks, DMA
> > channels, regulators) and on the of course outside of the SoC, on
> > the board.
> >
> > The question here is whether the way a hardware has instantiated
> > a certain IP block when doing physical compilation in their
> > Verilog, VHDL or SystemC files, is something that should be
> > described in DT.
> >
> > Many companies have developed tools to
> > extract this data from their hardware design files and provide
> > it to developers as a blob och incomprehensible data, such was
> > the situation for OMAP for example. So to them it made most
> > sense to implement pinctrl-single, just parsing that data into
> > DTS(I) files.
> >
> > Other companies (such as STMicroelectronics) instead put a
> > team of people to write a datasheet with a special chapter
> > on how pins etc are connected, and programmers are given
> > this datasheet and need to again type in the data and define
> > groups etc.
> >
> > Whether parametrization of a HW block should be done in the
> > driver file from the compatible string or with custom attributes
> > in the node is not a simple answer to the question. OF is vague
> > on this kind of things: both solutions exist.
> >
> > Allwinner and Qualcomm authors faced a situation such as that
> > they were given a code dump and no datasheet and no data
> > tables either. That creates an especially complicated situation
> > where none of the above scenarios apply.
> 
> Allwinner do give user manual about the pin controller, and they're
> used when we write the pinctrl-sunxi driver.

That has not always been true for all the SoCs, and it's still not the
case, even for newer SoCs.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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