linux-kernel - Re: [PATCH 1/2] ARM: multi_v7_defconfig: enable CONFIG_PWM

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Date:	Mon, 14 Mar 2016 13:18:24 +0100
From:	Thierry Reding <treding@...dia.com>
To:	Andy Yan <andy.yan@...nel-upstream.org>
CC:	<arnd@...db.de>, <javier@....samsung.com>, <kgene@...nel.org>,
	<k.kozlowski@...sung.com>, <geert+renesas@...der.be>,
	<linux-kernel@...r.kernel.org>, <public_timo.s@...entcreek.de>,
	<linux@....linux.org.uk>, <alexandre.belloni@...e-electrons.com>,
	<sjoerd.simons@...labora.co.uk>, <olof@...om.net>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] ARM: multi_v7_defconfig: enable CONFIG_PWM_ROCKCHIP=y

On Sat, Mar 12, 2016 at 08:50:29PM +0800, Andy Yan wrote:
> All the current rk3066 based boards use pwm modulate vdd_logic
> voltage, the board may hang when the system boot and run to a higher
> frequency without pwm enabled, so enable it as builtin.

I don't understand the rationale here. Surely if the system can't safely
switch to a higher frequency because the regulator isn't available, then
it should be prevented from switching, shouldn't it?

Making this change alone will not prevent users from switching this back
to =m on their own. So either you need to add code to prevent a switch
to an unsupported frequency in the absence of the regulator, or you need
to change the PWM_ROCKCHIP Kconfig option to be bool instead, though the
latter is of course a somewhat ugly hack, whereas the former would be a
proper fix.

Thierry

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