linux-kernel - Re: [PATCH v2 04/22] clk: qcom: smd-rpm: Export clock scaling availability

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Message-ID: <b7b1d19c-b87d-b3fd-36aa-374065a45ede@linaro.org>
Date:   Sat, 10 Jun 2023 20:53:05 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Leo Yan <leo.yan@...aro.org>,
        Evan Green <evgreen@...omium.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 04/22] clk: qcom: smd-rpm: Export clock scaling
 availability



On 10.06.2023 14:15, Konrad Dybcio wrote:
> 
> 
> On 10.06.2023 13:35, Stephan Gerhold wrote:
>> On Fri, Jun 09, 2023 at 10:19:09PM +0200, Konrad Dybcio wrote:
>>> Before we issue a call to RPM through clk_smd_rpm_enable_scaling() the
>>> clock rate requests will not be commited in hardware. This poses a
>>> race threat since we're accessing the bus clocks directly from within
>>> the interconnect framework.
>>>
>>> Add a marker to indicate that we're good to go with sending new requests
>>> and export it so that it can be referenced from icc.
>>>
>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>>> ---
>>>  drivers/clk/qcom/clk-smd-rpm.c   | 9 +++++++++
>>>  include/linux/soc/qcom/smd-rpm.h | 2 ++
>>>  2 files changed, 11 insertions(+)
>>>
>>> diff --git a/drivers/clk/qcom/clk-smd-rpm.c b/drivers/clk/qcom/clk-smd-rpm.c
>>> index 937cb1515968..482fe30ee6f0 100644
>>> --- a/drivers/clk/qcom/clk-smd-rpm.c
>>> +++ b/drivers/clk/qcom/clk-smd-rpm.c
>>> @@ -151,6 +151,7 @@
>>>  #define to_clk_smd_rpm(_hw) container_of(_hw, struct clk_smd_rpm, hw)
>>>  
>>>  static struct qcom_smd_rpm *rpmcc_smd_rpm;
>>> +static bool smd_rpm_clk_scaling;
>>>  
>>>  struct clk_smd_rpm {
>>>  	const int rpm_res_type;
>>> @@ -385,6 +386,12 @@ static unsigned long clk_smd_rpm_recalc_rate(struct clk_hw *hw,
>>>  	return r->rate;
>>>  }
>>>  
>>> +bool qcom_smd_rpm_scaling_available(void)
>>> +{
>>> +	return smd_rpm_clk_scaling;
>>> +}
>>> +EXPORT_SYMBOL_GPL(qcom_smd_rpm_scaling_available);
>>> +
>>>  static int clk_smd_rpm_enable_scaling(void)
>>>  {
>>>  	int ret;
>>> @@ -410,6 +417,8 @@ static int clk_smd_rpm_enable_scaling(void)
>>>  		return ret;
>>>  	}
>>>  
>>> +	smd_rpm_clk_scaling = true;
>>> +
>>
>> If you move the platform_device_register_data(&rpdev->dev,
>> "icc_smd_rpm", ...) from drivers/soc/qcom/smd-rpm.c to here you can
>> avoid the race completely and drop this API. I think that would be
>> cleaner. And it will likely probe much faster because probe deferral
>> is slow. :)
> Sounds like an idea.. especially since it's pretty much the only
> dependency other than SMDRPM itself!
It sounds great, but to not break bisecting one has to:

1. change the registration in soc/smd-rpm to store rpm ptr in driver
   data, in addition to parent driver data

2. change icc/smd-rpm to use the device and not parent data

3. add a platform_device_register_data call in clk-smd-rpm that will
   always fail because the device is always registered

4. remove the registration from soc/smd-rpm


I know you'd love to see me break my [PATCH xx/42] record, but I'd say
that deserves its own series and *this* patch could be a good transition
middleground :P

Hopefully Stephen, Bjorn and Georgi won't send a hitman after me for
abusing atomic cross-subsystem merges..

Konrad

> 
> Konrad
>>
>> Thanks,
>> Stephan