linux-kernel - Re: [PATCH] clk: tegra: Fix bypassing of PLLs

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Date:	Wed, 25 Nov 2015 07:52:13 -0800
From:	Tyler Baker <tyler.baker@...aro.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Jon Hunter <jonathanh@...dia.com>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-clk@...r.kernel.org, linux-tegra@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rhyland Klein <rklein@...dia.com>,
	"Kevin's boot bot" <khilman@...nel.org>
Subject: Re: [PATCH] clk: tegra: Fix bypassing of PLLs

On 25 November 2015 at 07:11, Thierry Reding <thierry.reding@...il.com> wrote:
> On Mon, Nov 23, 2015 at 03:18:59PM -0800, Tyler Baker wrote:
>> Hi Jon,
>>
>> On 20 November 2015 at 07:11, Jon Hunter <jonathanh@...dia.com> wrote:
>> > The _clk_disable_pll() function will attempt to place a PLL into bypass
>> > if the TEGRA_PLL_BYPASS is specified for the PLL and then disable the PLL
>> > by clearing the enable bit. To place the PLL into bypass, the bypass bit
>> > needs to be set and not cleared. Fix this by setting the bypass bit and
>> > not clearing it.
>> >
>> > Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>>
>> The kernelci.org bot recently detected a jetson-tk1 boot failure[1][2]
>> in the tegra tree. This boot failure has only been observed when
>> booting with a multi_v7_defconfig kernel variant. The bot bisected[3]
>> this boot failure to this commit, and I confirmed reverting it on top
>> of the tegra for-next branch resolves the issue. The ramdisk[4] used
>> for booting is loaded with the modules from the build. It appears to
>> me that as the modules are being loaded in userspace by eudev the
>> jetson-tk1 locks up. I've sifted through the console logs a bit, and
>> found this splat to be most interesting[5].  Can you confirm this
>> issue on your end?
>
> Just to close the loop on this: we've discussed this on IRC and came to
> the conclusion that not using the bypass mode is safer (switching into
> and out of bypass can glitch). I've dropped this patch for now and Jon
> will be looking into a second revision of the patch which, in addition
> to fixing bypass (the fix is legit, it just happens to break because of
> the glitch, most likely), will also remove the BYPASS flag setting so
> that bypass will not be used.

Thanks for the update, I appreciate you guys looking into this issue.
Please CC me on any fixes, I can re-test and give my tested-by.

Cheers,

Tyler
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