From mboxrd@z Thu Jan 1 00:00:00 1970 From: Taniya Das Subject: Re: [PATCH v6] clk: qcom: Add lpass clock controller driver for SDM845 Date: Fri, 19 Oct 2018 16:09:01 +0530 Message-ID: <5f1b1ab5-e2eb-05ff-7b6d-8557f6dd2ad9@codeaurora.org> References: <1538654546-31204-1-git-send-email-tdas@codeaurora.org> <1538654546-31204-2-git-send-email-tdas@codeaurora.org> <153896666821.119890.13143150697797456341@swboyd.mtv.corp.google.com> <153911832719.119890.11984877060665330428@swboyd.mtv.corp.google.com> <7d4012b9-e71d-f114-b228-7198f07ea767@codeaurora.org> <153936574404.5275.10513827793530511886@swboyd.mtv.corp.google.com> <7ad2344b-2307-3fb3-c34e-7443fb3a1ec8@codeaurora.org> <42e20a5e-beb4-fdc1-cf4a-f6329b09a476@codeaurora.org> <153978601529.5275.17218656685998024623@swboyd.mtv.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <153978601529.5275.17218656685998024623@swboyd.mtv.corp.google.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Stephen Boyd , Michael Turquette Cc: Andy Gross , David Brown , Rajendra Nayak , linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org On 10/17/2018 7:50 PM, Stephen Boyd wrote: > Quoting Taniya Das (2018-10-17 05:04:10) >> >> >> On 10/17/2018 5:07 PM, Taniya Das wrote: >>> Hello Stephen, >>> >>> On 10/12/2018 11:05 PM, Stephen Boyd wrote: >>>> Quoting Taniya Das (2018-10-09 23:12:27) >>>>> >>>>> >>>>> On 10/10/2018 2:22 AM, Stephen Boyd wrote: >>>>>> Quoting Taniya Das (2018-10-09 10:26:38) >>>>>>> Hello Stephen, >>>>>>> >>>>>>> On 10/8/2018 8:14 AM, Stephen Boyd wrote: >>>>>>>> Quoting Taniya Das (2018-10-04 05:02:26) >>>>>>>>> Add support for the lpass clock controller found on SDM845 based >>>>>>>>> devices. >>>>>>>>> This would allow lpass peripheral loader drivers to control the >>>>>>>>> clocks to >>>>>>>>> bring the subsystem out of reset. >>>>>>>>> LPASS clocks present on the global clock controller would be >>>>>>>>> registered >>>>>>>>> with the clock framework based on the device tree flag. Also do >>>>>>>>> not gate >>>>>>>>> these clocks if they are left unused. >>>>>>>> >>>>>>>> Why not gate them? This statement states what the code is doing, >>>>>>>> not why >>>>>>>> it's doing it which is the more crucial information that should be >>>>>>>> described in the commit text. Also, please add a comment about it >>>>>>>> to the >>>>>>>> code next to the flag. >>>>>>>> >>>>>>>> I am concerned that it doesn't make any sense though, so probably it >>>>>>>> shouldn't be marked as CLK_IGNORE_UNUSED and it's papering over some >>>>>>>> other larger bug that needs to be fixed. >>>>>>>> >>>>>>> >>>>>>> It does not have any bug, it is just that to access these lpass >>>>>>> registers we would need the GCC lpass registers to be enabled. I would >>>>>>> update the same in the commit text. >>>>>>> >>>>>>> During clock late_init these clocks should not be accessed to check >>>>>>> the >>>>>>> clock status as they would result in unclocked access. The client >>>>>>> would >>>>>>> request these clocks in the correct order and it would not have any >>>>>>> issue. >>>>>>> >>>>>> >>>>>> That seems like the bug right there. If the LPASS registers can't be >>>>>> accessed unless the clks in GCC are enabled then this driver needs to >>>>>> turn the clks on before reading/writing registers. Marking the clks as >>>>>> ignore unused is skipping around the real problem. >>>>>> >>>>> >>>>> If the driver requests for the clocks they would maintain the order. But >>>>> if the clock late init call is invoked before the driver requests, there >>>>> is no way I could manage this dependency, that is the only reason to >>>>> mark them unused. >>>>> >>>> >>>> Which driver are we talking about here? The lpass clk driver? Presumably >>>> the lpass clk driver would request the GCC clks and turn them on in >>>> probe and then register any lpass clks. If the lpass clk driver probes >>>> bfeore late init, then the gcc clks will be enabled and everything >>>> works, and if the lpass clk driver probes after late init then the clks >>>> that can't be touched without gcc clks enabled won't be registered, and >>>> then they won't be touched. What goes wrong? >>>> >>>> >>> >>> Okay, sure, I will take the GCC clock handles and then enable/disable >>> them accordingly. >>> >>> I missed earlier, so here is what you suggest >> >> gcc_probe --> GCC LPASS clocks registered. >> lpass_probe --> clk_get on gcc_lpass_clocks/ clk_prepare_enable --> >> register the lpass clocks --> clk_disable_unprepare gcc_lpass_clocks. > > Why did the gcc_lpass_clocks get turned off? Shouldn't they just stay > enabled all the time? > I don't think they are kept enabled all the time. >> >> But the problem is not during the above. It is the below >> static void clk_disable_unused_subtree(struct clk_core *core) >> { >> .... >> >> if (clk_core_is_enabled(core)) { --> This access fails. >> .... >> >> } >> > > You may need to add some prepare_ops to turn on clks needed to > read/write lpass registers. Or you can look into using some sort of > genpd to enable required clks when these clks are enabled or disabled. > But I suspect it would be easier to just leave the clks in GCC for lpass > always enabled and not worry about the complicated genpd things. > I need to check if keeping them enabled/marking them CRITICAL could have an impact on the reset of the subsystem. -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation. --