linux-kernel - Re: [PATCH] pinctrl-zynq: Initialize early

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Message-ID: <20151023054842.GV5257@xsjsorenbubuntu>
Date:	Thu, 22 Oct 2015 22:48:42 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Mike Looijmans <mike.looijmans@...ic.nl>
CC:	<git@...inx.com>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl-zynq: Initialize early

On Fri, 2015-10-23 at 07:43AM +0200, Mike Looijmans wrote:
> On 23-10-15 07:31, Mike Looijmans wrote:
> >On 22-10-15 18:07, Sören Brinkmann wrote:
> >>Hi Mike,
> >>
> >>On Thu, 2015-10-22 at 01:30PM +0200, Mike Looijmans wrote:
> >>>Supplying pinmux configuration for e.g. gpio pins leads to deferred
> >>>probes because the pinctrl device is probed much later than gpio.
> >>>Move the init call to a much earlier stage so it probes before the
> >>>devices that may need it.
> >>>
> >>>Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> >>
> >>in general, the change should be OK, but neither on zc702 nor zc706 do I
> >>see a difference in respect to deferred probes. With and without the
> >>patch I see:
> >>     root@...q:~# dmesg | grep -i defer
> >>     [    0.097021] zynq-gpio e000a000.gpio: could not find pctldev for node
> >>/amba/slcr@...00000/pinctrl@.../gpio0-default, deferring probe
> >>     root@...q:~#
> >>
> >>If you have a case this patch improves things though, feel free to add my
> >>Tested-by: Sören Brinkmann <soren.brinkmann@...inx.com>
> >>
> >
> >On the Florida boards there are i2c controlled clocks, power supplies and
> >reset signals. Replacing the Cadence I2C controller with a GPIO-bitbang
> >controller solved the I2C problems but caused a storm of dozens of deferred
> >probes because of the pinmux driver arriving even after the first probe
> >attempt of the i2c bus driver. Moving the pinmux driver to an earlier stage
> >solved that problem neatly, now the "zynq-pinctrl 700.pinctrl: zynq pinctrl
> >initialized" message appears after the OCM driver.
> >Judging from your comment the GPIO driver still probes earlier (I don't have
> >any GPIO-only pinmuxes yet), so maybe we should amend the patch to probe even
> >earlier. The pinmux driver doesn't depend on anything, so it can potentially
> >probe very early. What do you think?
> 
> Minor addition:
> The gpio-zynq driver probes at "postcore_initcall", so to beat that, the
> zynq-pinmux driver should move to "core_initcall" (instead of
> "arch_initcall"). That would make the gpio deferral go away.
> 
> An alternative would be to move the gpio driver to "arch", then "postcore"
> would be enough for the pinmux. If the gpio probe gets deferred, it
> apparently has already been moved to below "subsys" already, with aparently
> no ill effects.

Makes me wonder whether a single deferred probe is worth the risk of
breaking something by moving these things around. But probably worth a
try.

	Sören
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