Re: [PATCH v6] clk: qcom: Add lpass clock controller driver for SDM845

tdas
2018-10-25T10:51:04Z

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.