linux-kernel - Re: [PATCH v2] clk: exynos5420: Keep aclk66

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Message-ID: <CAD=FV=UZsEh+bOQxc8CP+yG5a5Sbp2eTyq8B_iq9u5io5G0B6A@mail.gmail.com>
Date:	Thu, 5 Jun 2014 12:22:27 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Tomasz Figa <tomasz.figa@...il.com>
Cc:	Tomasz Figa <t.figa@...sung.com>,
	Mike Turquette <mturquette@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Olof Johansson <olof@...om.net>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] clk: exynos5420: Keep aclk66_peric enabled during boot

Tomasz,

On Thu, Jun 5, 2014 at 12:14 PM, Tomasz Figa <tomasz.figa@...il.com> wrote:
> On 05.06.2014 20:48, Doug Anderson wrote:
>> Tomasz / Mike,
>>
>> On Fri, May 30, 2014 at 9:32 AM, Doug Anderson <dianders@...omium.org> wrote:
>>> Right now if you've got earlyprintk enabled on exynos5420-peach-pit
>>> then you'll get a hang on boot.  Here's why:
>>>
>>> 1. The i2c-s3c2410 driver will probe at subsys_initcall.  It will
>>>    enable its clock and disable it.  This is the clock "i2c2".
>>> 2. The act of disabling "i2c2" will disable its parents.  In this case
>>>    the parent is "aclk66_peric".  There are no other children of
>>>    "aclk66_peric" officially enabled, so "aclk66_peric" will be turned
>>>    off (despite being CLK_IGNORE_UNUSED, but that's by design).
>>> 3. The next time you try to earlyprintk you'll do so without the UART
>>>    clock enabled.  That's because the UART clocks are also children of
>>>    "aclk66_peric".  You'll hang.
>>>
>>> There's no good place to put a clock enable for earlyprintk, which is
>>> handled by a bunch of assembly code.  The best we can do is to handle
>>> this in the clock driver.
>>>
>>> Signed-off-by: Doug Anderson <dianders@...omium.org>
>>> Tested-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>
>>> ---
>>> Changes in v2:
>>> - Use GATE_A and clk_get().  Save the clock for putting later.
>>> - Return 0 from exynos5420_clk_late_init().
>>>
>>>  drivers/clk/samsung/clk-exynos5420.c | 33 +++++++++++++++++++++++++++++++--
>>>  1 file changed, 31 insertions(+), 2 deletions(-)
>>
>> Are there other changes you'd like me to make to this?  It would be
>> really nice to get this in for 3.16 so the system doesn't just
>> mysteriously hang when you use earlyprintk.
>
> We can probably take this as an -rc fix, so it should be fine.
>
> However I still don't see the point of exporting this clock and
> polluting the global clkdev namespace. Even the diffstat looks better in v1.

OK, I'm happy to go back to v1 with the addition of the "return 0".

Mike: are you OK with that?
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