linux-kernel - RE: [PATCH 2/2 v7] pinmux: add a driver for the U300 pinmux

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Message-ID: <74CDBE0F657A3D45AFBB94109FB122FF1738180164@HQMAIL01.nvidia.com>
Date:	Wed, 21 Sep 2011 12:39:46 -0700
From:	Stephen Warren <swarren@...dia.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Linus Walleij <linus.walleij@...ricsson.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Barry Song <21cnbao@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Joe Perches <joe@...ches.com>,
	Russell King <linux@....linux.org.uk>,
	Linaro Dev <linaro-dev@...ts.linaro.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	David Brown <davidb@...eaurora.org>
Subject: RE: [PATCH 2/2 v7] pinmux: add a driver for the U300 pinmux

Linus Walleij wrote at Wednesday, September 21, 2011 2:25 AM:
> On Wed, Sep 21, 2011 at 12:15 AM, Stephen Warren <swarren@...dia.com> wrote:
> > Linus Walleij wrote at Friday, September 16, 2011 6:14 AM:
> >> +     for (i = 0; i < ARRAY_SIZE(u300_mux_hogs); i++) {
> >> +             struct pinmux *pmx;
> >> +             int ret;
> >> +
> >> +             pmx = pinmux_get(u300_mux_hogs[i].dev, NULL);
> >> +             if (IS_ERR(pmx)) {
> >> +                     pr_err("u300: could not get pinmux hog %s\n",
> >> +                            u300_mux_hogs[i].name);
> >> +                     continue;
> >> +             }
> >> +             ret = pinmux_enable(pmx);
> >> +             if (ret) {
> >> +                     pr_err("u300: could enable pinmux hog %s\n",
> >> +                            u300_mux_hogs[i].name);
> >> +                     continue;
> >> +             }
> >> +             u300_mux_hogs[i].pmx = pmx;
> >> +     }
> >> +     return 0;
> >> +}
> >> +subsys_initcall(u300_pinmux_fetch);
> >
> > Why not just have the pinmux core support hogging on non-"system" mapping
> > entries; then everything I quoted above except u300_pinmux_map[] could
> > be deleted, and the "hog" flag set on the last 3 u300_pinmux_map[] entries.
> 
> Very good question, luckily I have a good answer.
> 
> There is no way for the pinmux core to traverse the system and look
> up the apropriate struct device * pointers.

It's unclear to me why that would be needed.

For non-system mappings, either the device-driver in question will be
get'ing and enabling them (this case isn't relevant to this discussion),
or they'll be hogged. In the hog case, I doubt anything would ever want
to disable them and switch the device to a different mapping entry; if
that were the case, the entries shouldn't be hogged, but get/enabled by
the device anyway. Hence, I don't see the need for an activation of a
hog'd non-system mapping entry to care about the device fields that are
in the mapping table at all; they could just be ignored couldn't they?

> When/if we have device tree support, I think this will be possible, then I
> will be able to have the pinmux hog look up devices from device tree
> and hog their pinmux.
> 
> At that point we'll likely have the mapping in the device tree too and
> the core does not need to be involved at all.
> 
> What I could do right now is add some open-ended function like
> pinmux_hog_device_pinmuxes(struct device **devices);
> that can take an array of devices and hog their respective
> pinmuxes in the hog list. Do you think it's a good idea?

-- 
nvpublic

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