From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rajendra Nayak Date: Wed, 27 Jun 2012 05:31:24 +0000 Subject: Re: [PATCH 05/11] OMAPDSS: add clk_prepare and clk_unprepare Message-Id: <4FEA97DC.4070902@ti.com> List-Id: References: <1340372890-10091-1-git-send-email-rnayak@ti.com> <1340372890-10091-6-git-send-email-rnayak@ti.com> <1340604478.12683.25.camel@lappyti> <4FE80C43.6090802@ti.com> <1340611133.3395.3.camel@deskari> <4FE85005.4090303@ti.com> <1340630090.3395.85.camel@deskari> <20120627004709.GA22766@gmail.com> <1340770798.1972.4.camel@lappyti> In-Reply-To: <1340770798.1972.4.camel@lappyti> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-arm-kernel@lists.infradead.org On Wednesday 27 June 2012 09:49 AM, Tomi Valkeinen wrote: > On Tue, 2012-06-26 at 17:47 -0700, Mike Turquette wrote: >> On 20120625-16:14, Tomi Valkeinen wrote: >>> A question about clk_prepare/unprepare, not directly related: let's say >>> I have a driver for some HW block. The driver doesn't use clk functions, >>> but uses runtime PM. The driver also sets pm_runtime_irq_safe(). >>> >>> Now, the driver can call pm_runtime_get_sync() in an atomic context, and >>> this would lead to the underlying framework (hwmod, omap_device, I don't >>> know who =) enabling the func clock for that HW. But this would happen >>> in atomic context, so the underlying framework can't use clk_prepare. >>> >>> How does the underlying framework handle that case? (sorry if that's a >>> stupid question =). >>> >> >> I think it's a good question! >> >> If we're going to call clk_prepare_enable from within a runtime pm >> callback then I think we'll need to check if _irq_safe() is set and >> conditionally call only clk_enable in such a case. >> >> I'm not a runtime pm expert, but if the driver owns the responsibility >> of calling pm_runtime_irq_safe then the driver has the proper context >> to know that it should call clk_prepare BEFORE calling >> pm_runtime_get_sync. > > That's not quite what I meant. If it's the driver that does clk_enable, > be it in runtime PM callback or not, it's driver's responsibility. > > But some clocks are not handled by the driver, but the hwmod/omap_device > framework. Mainly I think this is for the functional and interface > clocks. The driver has no visibility to those, they are implicitly > enabled via pm_runtime_get. yes, thats the tricky part on how would hwmod/omap_device know if the driver would use runtime pm within atomic context or non-atomic context. The driver does inform the runtime pm framework about this by calling a pm_runtime_irq_safe(), which is then used to set the .irq_safe flag telling it to leave the interrupts disabled during callbacks. This information however does not flow down to hwmod/omap_device in any way. So the way its currently handled is to do an early prepare of all hwmod controlled clocks. I have copied Kevin in case he has any better ideas on how this should be handled. > > Tomi >