linux-kernel - Re: [PATCH V4 16/16] ARM64: tegra: select PM_GENERIC

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Date:	Wed, 16 Dec 2015 09:40:50 +0000
From:	Jon Hunter <jonathanh@...dia.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>
CC:	Philipp Zabel <p.zabel@...gutronix.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	"Alexandre Courbot" <gnurou@...il.com>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...nel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Vince Hsu <vinceh@...dia.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH V4 16/16] ARM64: tegra: select PM_GENERIC_DOMAINS

Hi Ulf,

On 15/12/15 19:54, Ulf Hansson wrote:
> On 4 December 2015 at 15:57, Jon Hunter <jonathanh@...dia.com> wrote:
>> Enable PM_GENERIC_DOMAINS for tegra 64-bit devices. To ensure that devices
>> dependent upon a particular power-domain are only probed when that power
>> domain has been powered up, requires that PM is made mandatory for tegra
>> 64-bit devices and so select this option for tegra as well.
>>
>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>> ---
>>  arch/arm64/Kconfig.platforms | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/arm64/Kconfig.platforms b/arch/arm64/Kconfig.platforms
>> index 9806324fa215..e0b5bd0aff0f 100644
>> --- a/arch/arm64/Kconfig.platforms
>> +++ b/arch/arm64/Kconfig.platforms
>> @@ -93,6 +93,8 @@ config ARCH_TEGRA
>>         select GENERIC_CLOCKEVENTS
>>         select HAVE_CLK
>>         select PINCTRL
>> +       select PM
>> +       select PM_GENERIC_DOMAINS
> 
> If you still want to allow ARCH_TEGRA to run without PM, you should
> probably change to:
> 
> select PM_GENERIC_DOMAINS if PM

Per the changelog this is deliberate. If we allow !PM, then there is a
potential that you could probe a device when the power domain is not
powered on. I understand that some SoCs turn on all the power-domains
when !PM but this will not work for tegra because we don't register the
power domain until later in the boot and so we are relying upon probe
deferral to defer the probe of devices that use power-domains.

Cheers
Jon
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