> On 05/08/2012 10:15 AM, Turquette, Mike wrote: >> On Mon, May 7, 2012 at 10:07 PM, zhoujie wu<zhoujiewu@xxxxxxxxx> wrote: >>> Hi Mike, >>> Could you please explain more details about how to implement a >>> re-parenting operation as part of it's .set_rate implementation? >> >> Sure. >> >>> As far as I know, we can not call clk_set_parent in .set_rate function >>> directly, since clk_set_rate and clk_set_parent are using the same >>> prepare_lock. >> >> That is correct. >> >>> Any other interface can be used to implement it? >> >> You have two options available to you. >> >> 1) __clk_reparent can be used from your .set_rate callback today to >> reflect changes made to the tree topology. OMAP uses this in our PLL >> .set_rate implementation: depending on the re-lock frequency the PLL >> may switch parents dynamically. __clk_reparent does the >> framework-level cleanup needed for this (that function is also used >> when populating the clock tree with new clock nodes). >> >> 2) __clk_set_parent could be made non-static if you needed this (I've >> been meaning to talk to Saravana about this since I think MSM needs >> something like this). > > Thanks! > > I don't think I need (2). But I don't think I can use (1) as is either. > I can use (1) with some additional code in my set rate op. > > While set rate is in progress, both the parents might need to stay > enabled for a short duration. So, in my internal set rate, I need to > check if my clock is prepared/enabled and call prepare/enable on the > "old parent", call __clk_reparent (which will reduce the ref count for > the old parents and increase it for the new parents), finish the > reparent in HW and then unprepare/disable the old parent if I have > prepared/enabled them earlier. > > It might be beneficial to provide something like a > __clk_reparent_start(new_parent, *scratch_pointer) and > __clk_reparent_finish(*scratch_pointer) if it will be useful for more > than just MSM. Based on this email, I would guess that Tegra would want > something similar too. Thinking more about this, I think this is how any clk op that might change the parent should operate. I will try to write up an RFC patch for this and send it out soon. I'm in a hurry, so will explain more in the RFC patch or in a later email. Thanks, Saravana -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
