From mboxrd@z Thu Jan 1 00:00:00 1970 From: tdas@codeaurora.org Subject: Re: [PATCH v6] clk: qcom: Add lpass clock controller driver for SDM845 Date: Thu, 25 Oct 2018 16:21:01 +0530 Message-ID: <360c18d625d6e4792e9ba830c6d0b6ea@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> <5f1b1ab5-e2eb-05ff-7b6d-8557f6dd2ad9@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5f1b1ab5-e2eb-05ff-7b6d-8557f6dd2ad9@codeaurora.org> 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, linux-clk-owner@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org On 2018-10-19 16:09, Taniya Das wrote: > 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. I have checked internally with the teams and the GCC LPASS clocks could be left enabled. Would submit a patch keeping them CRITICAL.