linux-kernel - Re: [PATCH 2/2] clk: qcom: gcc-msm8996: Use read-only RCG ops for RPM bus clocks

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Date:   Mon, 12 Jun 2023 13:46:26 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] clk: qcom: gcc-msm8996: Use read-only RCG ops for RPM
 bus clocks



On 12.06.2023 12:17, Stephan Gerhold wrote:
> On Mon, Jun 12, 2023 at 11:22:48AM +0200, Konrad Dybcio wrote:
>> The config/periph/system NoC clocks are wholly controlled by the
>> RPM firmware and Linux should never ever alter their configuration.
>>
>> Switch them over to read-only ops to avoid that.
>>
>> Fixes: b1e010c0730a ("clk: qcom: Add MSM8996 Global Clock Control (GCC) driver")
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>> ---
>>  drivers/clk/qcom/gcc-msm8996.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/clk/qcom/gcc-msm8996.c b/drivers/clk/qcom/gcc-msm8996.c
>> index 5e44d1bcca9e..588e3b67657a 100644
>> --- a/drivers/clk/qcom/gcc-msm8996.c
>> +++ b/drivers/clk/qcom/gcc-msm8996.c
>> @@ -264,7 +264,7 @@ static struct clk_rcg2 system_noc_clk_src = {
>>  		.name = "system_noc_clk_src",
>>  		.parent_data = gcc_xo_gpll0_gpll0_early_div,
>>  		.num_parents = ARRAY_SIZE(gcc_xo_gpll0_gpll0_early_div),
>> -		.ops = &clk_rcg2_ops,
>> +		.ops = &clk_rcg2_ro_ops,
>>  	},
>>  };
>>  
>> @@ -284,7 +284,7 @@ static struct clk_rcg2 config_noc_clk_src = {
>>  		.name = "config_noc_clk_src",
>>  		.parent_data = gcc_xo_gpll0,
>>  		.num_parents = ARRAY_SIZE(gcc_xo_gpll0),
>> -		.ops = &clk_rcg2_ops,
>> +		.ops = &clk_rcg2_ro_ops,
>>  	},
>>  };
>>  
>> @@ -306,7 +306,7 @@ static struct clk_rcg2 periph_noc_clk_src = {
>>  		.name = "periph_noc_clk_src",
>>  		.parent_data = gcc_xo_gpll0,
>>  		.num_parents = ARRAY_SIZE(gcc_xo_gpll0),
>> -		.ops = &clk_rcg2_ops,
>> +		.ops = &clk_rcg2_ro_ops,
>>  	},
>>  };
>>  
> 
> If the rcg is read-only then it shouldn't need a .freq_tbl (the
> .recalc_rate() works without it). These clocks have one for some reason.
.get_parent needs it

> 
> Maybe we should also set .flags = CLK_GET_RATE_NOCACHE to ensure that
> clk_get_rate() doesn't return some stale value? Although I'm not sure if
> it's enough to set it here or if it would need to be set on all child
> clocks as well.
Hm, I'm not sure if it makes sense for the children..

Konrad

> 
> Thanks,
> Stephan