linux-kernel - Re: [RFC PATCH] slimbus: Linux driver framework for SLIMbus.

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Date:	Wed, 24 Aug 2011 11:15:56 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Kenneth Heitke <kheitke@...eaurora.org>,
	sdharia@...eaurora.org, David Brown <davidb@...eaurora.org>,
	bryanh@...eaurora.org, linux-arm-msm@...r.kernel.org,
	rdunlap@...otime.net, rmk+kernel@....linux.org.uk,
	john.stultz@...aro.org, akpm@...ux-foundation.org, ohad@...ery.com,
	gregkh@...e.de, stefanr@...6.in-berlin.de, lethal@...ux-sh.org,
	linville@...driver.com, zajec5@...il.com,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] slimbus: Linux driver framework for SLIMbus.

On Thu, Aug 18, 2011 at 5:00 AM, Mark Brown
<broonie@...nsource.wolfsonmicro.com> wrote:
> On Wed, 2011-08-17 at 15:17 +0200, Linus Walleij wrote:
>> On Wed, Aug 17, 2011 at 3:04 PM, Mark Brown
>> <broonie@...nsource.wolfsonmicro.com> wrote:
>
>> > The device driver will know what power supplies and other signals the
>> > device has, and it will know how and when to use them. (...)
>
>> And I guess there is nothing in the spec claiming that all devices
>> be powered-on when you boot?
>
> I don't believe so, and if there were I'd not expect anyone to pay a
> blind bit of notice to it.

That means that the regulators handling the slimbus devices
will need to be enabled before the drivers issue regulator_get()
and regulator_enable() on them.

Does the regulator constraint .always_on have this semantic
effect, so the regulator framework can power up the devices
without their drivers claiming the regulators first?

Or would we need a new .boot_enable flag to handle that?

> If my memory serves (I don't have access to the relevant documents right
> now) the device announces itself when it detects that the bus is alive.
> Slimbus is a relatively heavyweight interface so the extra cost of doing
> this won't be too bad.

OK so if we can just power the device the bus can probably
autodetect all devices on it, it seems.

Thanks,
Linus Walleij
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