linux-kernel - Re: [PATCH v2 1/3] arm64: imx8mq: add imx8mq iomux-gpr field defines

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Date:   Tue, 13 Aug 2019 13:07:52 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Guido Günther <agx@...xcpu.org>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Lee Jones <lee.jones@...aro.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Robert Chiras <robert.chiras@....com>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v2 1/3] arm64: imx8mq: add imx8mq iomux-gpr field defines

On Tue, Aug 13, 2019 at 12:10 PM Guido Günther <agx@...xcpu.org> wrote:
> On Tue, Aug 13, 2019 at 10:08:44AM +0200, Arnd Bergmann wrote:
> > On Fri, Aug 9, 2019 at 6:24 PM Guido Günther <agx@...xcpu.org> wrote:
> > >
> > > This adds all the gpr registers and the define needed for selecting
> > > the input source in the imx-nwl drm bridge.
> > >
> > > Signed-off-by: Guido Günther <agx@...xcpu.org>
> > > +
> > > +#define IOMUXC_GPR0    0x00
> > > +#define IOMUXC_GPR1    0x04
> > > +#define IOMUXC_GPR2    0x08
> > > +#define IOMUXC_GPR3    0x0c
> > > +#define IOMUXC_GPR4    0x10
> > > +#define IOMUXC_GPR5    0x14
> > > +#define IOMUXC_GPR6    0x18
> > > +#define IOMUXC_GPR7    0x1c
> > (more of the same)
> >
> > huh?
>
> These are the names from the imx8MQ reference manual (general purpose
> registers, they lump together all sorts of things), it's the same on
> imx6/imx7):
>
>     https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/mfd/syscon/imx6q-iomuxc-gpr.h
>     https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/mfd/syscon/imx7-iomuxc-gpr.h
>
> > > +/* i.MX8Mq iomux gpr register field defines */
> > > +#define IMX8MQ_GPR13_MIPI_MUX_SEL              BIT(2)
> >
> > I think this define should probably be local to the pinctrl driver, to
> > ensure that no other drivers fiddle with the registers manually.
>
> The purpose of these bits is for a driver to fiddle with them to select
> the input source. Similar on imx7 it's already used for e.g. the phy
> refclk in the pci controller:
>
>     https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/dwc/pci-imx6.c#n638

That one should likely use either the clk interface or the phy
interface instead.

> The GPRs are not about pad configuration but gather all sorts of things
> (section 8.2.4 of the imx8mq reference manual): pcie setup, dsi related
> bits so I don't think this should be done via a pinctrl
> driver. Should we handle that differently than on imx6/7?

It would be nice to fix the existing code as well, but for the moment,
I only think we should not add more of that.

Generally speaking, we can use syscon to do random things that don't
have a subsystem of their own, but we should not use it to do things
that have an existing driver framework like pinctrl, clock, reset, phy
etc.

       Arnd