Re: [PATCH] PM / devfreq: tegra30: disable clock on error in probe

Chanwoo Choi
2020-09-17T02:27:11Z

On 9/17/20 4:07 AM, Dmitry Osipenko wrote:
> 16.09.2020 05:38, Chanwoo Choi пишет:
>> On 9/16/20 2:01 AM, Dmitry Osipenko wrote:
>>> 15.09.2020 05:13, Chanwoo Choi пишет:
>>>> On 9/15/20 11:00 AM, Chanwoo Choi wrote:
>>>>> Hi Dmitry,
>>>>>
>>>>> On 9/14/20 10:56 PM, Dmitry Osipenko wrote:
>>>>>> 14.09.2020 10:09, Chanwoo Choi пишет:
>>>>>>> Hi,
>>>>>>>
>>>>>>> On 9/8/20 4:25 PM, Dan Carpenter wrote:
>>>>>>>> This error path needs to call clk_disable_unprepare().
>>>>>>>>
>>>>>>>> Fixes: 7296443b900e ("PM / devfreq: tegra30: Handle possible round-rate error")
>>>>>>>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>>>>>>>> ---
>>>>>>>> ---
>>>>>>>> drivers/devfreq/tegra30-devfreq.c | 4 +++-
>>>>>>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/devfreq/tegra30-devfreq.c b/drivers/devfreq/tegra30-devfreq.c
>>>>>>>> index e94a27804c20..dedd39de7367 100644
>>>>>>>> --- a/drivers/devfreq/tegra30-devfreq.c
>>>>>>>> +++ b/drivers/devfreq/tegra30-devfreq.c
>>>>>>>> @@ -836,7 +836,8 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>>>>>>>> rate = clk_round_rate(tegra->emc_clock, ULONG_MAX);
>>>>>>>> if (rate < 0) {
>>>>>>>> dev_err(&pdev->dev, "Failed to round clock rate: %ld\n", rate);
>>>>>>>> - return rate;
>>>>>>>> + err = rate;
>>>>>>>> + goto disable_clk;
>>>>>>>> }
>>>>>>>>
>>>>>>>> tegra->max_freq = rate / KHZ;
>>>>>>>> @@ -897,6 +898,7 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>>>>>>>> dev_pm_opp_remove_all_dynamic(&pdev->dev);
>>>>>>>>
>>>>>>>> reset_control_reset(tegra->reset);
>>>>>>>> +disable_clk:
>>>>>>>> clk_disable_unprepare(tegra->clock);
>>>>>>>
>>>>>>> Is it doesn't need to reset with reset_contrl_reset()?
>>>>>>
>>>>>> Hello, Chanwoo!
>>>>>>
>>>>>> It's reset just before the clk_round_rate() invocation, hence there
>>>>>> shouldn't be a need to reset it second time.
>>>>>
>>>>> Do you mean that reset is deasserted automatically
>>>>> when invoke clk_round_rate() on tegra?
>>>
>>> I only mean that the tegra30-devfreq driver deasserts the reset before
>>> the clk_round_rate():
>>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/devfreq/tegra30-devfreq.c?h=v5.9-rc5#n834
>>>
>>>>> If tree, I think that 'reset_control_reset(tegra->reset)' invocation
>>>>
>>>> I'm sorry for my typo. s/tree/true.
>>>>
>>>>> is not needed on 'remove_opp:' goto. Because already reset deassertion
>>>>> is invoked by clk_round_rate(), it seems that doesn't need to invoke
>>>>> anymore during exception case.
>>>>>
>>>>> Actually, it is not clear in my case.
>>>
>>> The reset_control_reset() in the error path of the driver probe function
>>> is placed that way to make the tear-down order match the driver removal
>>> order. Perhaps the reset could be moved before the remove_opp, but this
>>> change won't make any real difference, hence it already should be good
>>> as-is.
>>>
>>>
>>
>> I have one more question.
>> When failed to enable clock on line829[1],
>> does it need any reset_control invocation?
>> In this case on line829, just return without any restoration
>> about reset control.
>>
>> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/devfreq/tegra30-devfreq.c?h=v5.9-rc5#n829
>>
>
> There is no need to deassert the reset if clk-enable fails because reset
> control of tegra30-devfreq is exclusive, i.e it isn't shared with any
> other peripherals, and thus, reset control could asserted/deasserted at
> any time by the devfreq driver. If clk-enable fails, then reset will
> stay asserted and it will be fine to re-assert it again.
>

Thanks for the detailed explanation.
But, I think that almost people don't know the detailed h/w information.
If possible, how about matching the pair when clk-enable fails as following?

--- a/drivers/devfreq/tegra30-devfreq.c
+++ b/drivers/devfreq/tegra30-devfreq.c
@@ -828,6 +828,7 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
if (err) {
dev_err(&pdev->dev,
"Failed to prepare and enable ACTMON clock\n");
+ reset_control_deassert(tegra->reset);
return err;
}

--
Best Regards,
Chanwoo Choi
Samsung Electronics