From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arend van Spriel Subject: Re: RFC: representing sdio devices oob interrupt, clks, etc. in device tree Date: Fri, 23 May 2014 15:21:34 +0200 Message-ID: <537F4B5E.80306@broadcom.com> References: <537DC832.3020006@redhat.com> <537DE1AA.5050606@redhat.com> <537E31F7.1030505@gmail.com> <537F1148.3010102@redhat.com> <20140523112239.GB12304@sirena.org.uk> <537F3610.3050104@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <537F3610.3050104@redhat.com> Sender: linux-mmc-owner@vger.kernel.org To: Hans de Goede Cc: Mark Brown , Tomasz Figa , Chen-Yu Tsai , Sascha Hauer , Chris Ball , Ulf Hansson , Maxime Ripard , linux-mmc , linux-arm-kernel , devicetree , Olof Johansson , Russell King - ARM Linux , Fabio Estevam , Arnd Bergmann , Jyri Sarha List-Id: devicetree@vger.kernel.org On 05/23/14 13:50, Hans de Goede wrote: > Hi, > > On 05/23/2014 01:22 PM, Mark Brown wrote: >> On Fri, May 23, 2014 at 11:13:44AM +0200, Hans de Goede wrote: >> >>> Thinking more about this, I would like to make one change to my >>> proposal, the mmc-core should only do power up of child-nodes if >>> they have a compatible of: "simple-sdio-powerup". This way >>> when we add something more complex, we can keep the simple powerup >>> code in the mmc core, keeping what we've already using this working >>> and the mmc core won't respond to the child nodes for more complex >>> devices, so it won't conflict with more complex power-up handling >>> handled by some other driver. >> >> Would it not be better to have this be something in the driver struct >> rather than in the device tree? Putting a compatible in there would be >> encoding details of the Linux implementation in the DT which doesn't >> seem right especially since these are details we're thinking of changing >> later on. > > The compatible is not a Linux specific thing, it is a marking saying > that something needs to take care of enabling the clks (and whatever > else we will make part of the binding for this compatible), before > scanning the mmc bus. > >> Something like have the driver set flags saying if it wants >> to do complicated things. > > Chicken<-> egg, we won't know which driver to use before we've probed > the mmc bus, and we cannot probe the bus before enabling the clks, etc. The approach I took with brcmfmac is that upon module init I search the DT for "brcm,bcm43xx-fmac" compatible and get the clock and/or gpio resource and enable them before registering the sdio driver. The difficulty is probably when using the driver built-in as the clocks and gpios may not be available yet and we can not rely on deferred probing in module init stage. Regards, Arend >>> FWIW if we ever get truely complex cases I think modeling the >>> power-up hardware as a pmic platform device is not a bad idea, >>> we would then need to have a generic mmc-host pmic property, which >>> would be used both to do the initial powerup before scanning, as >>> well as for the sdio device driver to get a handle to the pmic, >>> for run time power-management (if desired). >> >> I don't know if this will ever apply to SDIO but with other buses the >> complicated bits come when the driver wants to take over some of the >> power management do things like turn some of the supplies or clocks on >> and off independently at runtime for low power modes. > > Hmm, good point in that case actually having these things in the > child node makes most sense, because then the driver can find them > their. Note that the mmc core enabling things does not mean that > the driver cannot later disable them if needed.