Re: [PATCH] regulator: core: Skip balancing of the enabled regulators in regulator_enable()

From: Marek Szyprowski <m.szyprowski@samsung.com>
To: Mark Brown <broonie@kernel.org>
Cc: linux-kernel@vger.kernel.org, Dmitry Osipenko <digetx@gmail.com>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Lucas Stach <l.stach@pengutronix.de>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	linux-samsung-soc@vger.kernel.org
Subject: Re: [PATCH] regulator: core: Skip balancing of the enabled regulators in regulator_enable()
Date: Tue, 8 Oct 2019 14:01:15 +0200	[thread overview]
Message-ID: <0e222fdd-4407-51ea-b75c-a62621cbe622@samsung.com> (raw)
In-Reply-To: <20191008115025.GF4382@sirena.co.uk>

Hi Mark,

On 08.10.2019 13:50, Mark Brown wrote:
> On Tue, Oct 08, 2019 at 12:17:09PM +0200, Marek Szyprowski wrote:
>> Commit f8702f9e4aa7 ("regulator: core: Use ww_mutex for regulators
>> locking"), regardless of the subject, added additional call to
>> regulator_balance_voltage() during regulator_enable(). This is basically
>> a good idea, however it causes some issue for the regulators which are
>> already enabled at boot and are critical for system operation (for example
>> provides supply to the CPU).
> If regulators are essential to system operation they should be marked as
> always-on...

The are marked as always on:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/exynos5800-peach-pi.dts#n253

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/exynos5800-peach-pi.dts#n265

>> CPUfreq or other drivers typically call regulator_enable() on such
>> regulators during their probe, although the regulators are already enabled
>> by bootloader. The mentioned patch however added a call to
>> regulator_balance_voltage(), what in case of system boot, where no
>> additional requirements are set yet, typically causes to limit the voltage
>> to the minimal value defined at regulator constraints. This causes a crash
>> of the system when voltage on the CPU regulator is set to the lowest
>> possible value without adjusting the operation frequency. Fix this by
>> adding a check if regulator is already enabled - if so, then skip the
>> balancing procedure. The voltage will be balanced later anyway once the
>> required voltage value is requested.
> This then means that for users that might legitimately enable and
> disable regulators that need to be constrained are forced to change the
> voltage when they enable the regualtors in order to have their
> constraints take effect which seems bad.  I'd rather change the the
> cpufreq consumers to either not do the enable (since there really should
> be an always-on constraint this should be redundant, we might need to
> fix the core to take account of their settings though I think we lost
> that) or to set the voltage to whatever they need prior to doing their
> first enable, that seems more robust.

Well, I'm open for other ways of fixing this issue. Calling enable on 
always-on regulator imho should not change its rate...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland