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

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Date:   Sat, 10 Jun 2023 14:15:07 +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 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!

Konrad
> 
> Thanks,
> Stephan