Messages in this thread | | | Date | Thu, 25 Oct 2018 16:21:01 +0530 | From | tdas@codeauro ... | Subject | Re: [PATCH v6] clk: qcom: Add lpass clock controller driver for SDM845 |
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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.
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