linux-kernel - Re: [PATCH v4 2/3] pinctrl: exynos: Fix GPIO setup failure because domain clock being gated

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Date:	Mon, 05 Jan 2015 15:15:30 +0100
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Tomasz Figa <tomasz.figa@...il.com>,
	Mike Turquette <mturquette@...aro.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Kukjin Kim <kgene@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	Kevin Hilman <khilman@...nel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v4 2/3] pinctrl: exynos: Fix GPIO setup failure because
 domain clock being gated

On pon, 2015-01-05 at 15:05 +0100, Linus Walleij wrote:
> On Fri, Dec 5, 2014 at 12:00 PM, Krzysztof Kozlowski
> <k.kozlowski@...sung.com> wrote:
> 
> > The audio subsystem on Exynos 5420 has separate clocks and GPIO. To
> > operate properly on GPIOs the main block clock 'mau_epll' must be
> > enabled.
> >
> > This was observed on Peach Pi/Pit and Arndale Octa (after enabling i2s0)
> > after introducing runtime PM to pl330 DMA driver. After that commit the
> > 'mau_epll' was gated, because the "amba" clock was disabled and there
> > were no more users of mau_epll.
> >
> > The system hang just before probing i2s0 because
> > samsung_pinmux_setup() tried to access memory from audss block which was
> > gated.
> >
> > Add a clock property to the pinctrl driver and enable the clock during
> > GPIO setup. During normal GPIO operations (set, get, set_direction) the
> > clock is not enabled.
> >
> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> > Tested-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>
> 
> Tomasz, is this OK and should I apply it for fixes or next?

Ha! That is a good question. The issue is fixed for now by the
workaround (merged) [1].

The workaround just enables the clock for entire runtime of Exynos
5420-like device. This has some energy impact - around 1.5% in idle [2].

So actually this is question which way we want to solve it:
1. Stick with the workaround (small piece of code, energy impact when
not used).
2. Full clock enable on use (big chunk of code, no energy impact when
not used).

[1]
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f1e9203e2366164b832d8a6ce10134de8c575178
[2] http://www.spinics.net/lists/linux-samsung-soc/msg39827.html

Best regards,
Krzysztof


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