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Message-ID: <532C4816.2080102@st.com> Date: Fri, 21 Mar 2014 15:09:26 +0100 From: Maxime Coquelin <maxime.coquelin@...com> To: Mike Turquette <mturquette@...aro.org>, Sylwester Nawrocki <s.nawrocki@...sung.com>, <linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org> Cc: <mark.rutland@....com>, <gregkh@...uxfoundation.org>, <t.figa@...sung.com>, <sw0312.kim@...sung.com>, <linux-kernel@...r.kernel.org>, <kyungmin.park@...sung.com>, <robh+dt@...nel.org>, <galak@...eaurora.org>, <grant.likely@...aro.org>, <linux@....linux.org.uk>, <m.szyprowski@...sung.com>, <t-kristo@...com> Subject: Re: [RFC PATCH v2 0/2] clk: Support for DT assigned clock parents and rates Hi Mike, On 03/21/2014 02:45 AM, Mike Turquette wrote: > Quoting Sylwester Nawrocki (2014-03-20 05:42:33) >> Hi Maxime, >> >> On 06/03/14 14:45, Maxime Coquelin wrote: >>> Hi Sylwester, >>> >>> I like the principle of your implementation, but I have two questions: >>> 1 - How can we manage PM with this solution, as the parent/rate will be >>> set only once at probe time? >>> 2 - How to set the parent of a parent clock (which can be shared with >>> other devices)? Same question about the parent rates. >> >> Thanks for your feedback and apologies for late reply. >> >> IIUC your first concern is about a situation when clocks need to be >> reconfigured upon each resume from system sleep or runtime PM resume ? >> As I mentioned in v1 of the RFC I was considering having individual >> drivers calling explicitly the clocks set up routine. Presumably this >> would allow to resolve the power management related issue. >> One example I'm aware the approach as in this RFC wouldn't work is >> when a device in a SoC belongs to a power domain, which needs to be >> first switched on before we can start setting up and the clocks' >> configuration get lost after the power domain switch off. > > I like Sylwester's approach of handling this one-time setup in the > driver core. > > Any kind of fine grained power management should not be hidden by DT, > and by definition that logic belongs in the device driver. It can still > be nicely abstracted away by runtime pm[1]. > > Regards, > Mike > > [1] Message-ID: <20140320114238.GQ7528@...00.arm.linux.org.uk> How can I access this reference? Thanks, Maxime > >> >> OTOH I suspect devices for which one-time clocks setup is sufficient >> will be quite common. And for these there would need to be a single >> call to the setup routine in probe() I guess, since it wouldn't be >> possible to figure out just from the DT data when the actual call >> should be made. >> >> For a global clocks configuration, I thought about specifying that >> in the clocks controller node, and then to have the setup routine >> called e.g. from of_clk_init(). I think that could work well enough, >> together with the patch [1], adding clock dependencies handling. >> But then the clock frequency set up function would need to be >> modified to respect the clock parent relationships, similarly as >> in patch series [2]. A just noticed [2] recently, after posting >> this RFC (adding Tero at Cc). >> >> -- >> Regards, >> Sylwester >> >> [1] http://www.spinics.net/lists/arm-kernel/msg310507.html >> [2] http://www.spinics.net/lists/linux-omap/msg103069.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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