linux-kernel - Re: [PATCH 6/6] clk: qcom: Fix APSS PLL and RCG Configuration

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Date:   Tue, 31 Jan 2023 14:53:19 +0530
From:   Devi Priya <quic_devipriy@...cinc.com>
To:     Robert Marko <robimarko@...il.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>, <agross@...nel.org>,
        <andersson@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <mturquette@...libre.com>,
        <sboyd@...nel.org>, <jassisinghbrar@...il.com>,
        <catalin.marinas@....com>, <will@...nel.org>,
        <shawnguo@...nel.org>, <arnd@...db.de>,
        <marcel.ziswiler@...adex.com>, <dmitry.baryshkov@...aro.org>,
        <nfraprado@...labora.com>, <broonie@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
CC:     <quic_srichara@...cinc.com>, <quic_gokulsri@...cinc.com>,
        <quic_sjaganat@...cinc.com>, <quic_kathirav@...cinc.com>,
        <quic_arajkuma@...cinc.com>, <quic_anusha@...cinc.com>,
        <quic_poovendh@...cinc.com>, <quic_ipkumar@...cinc.com>
Subject: Re: [PATCH 6/6] clk: qcom: Fix APSS PLL and RCG Configuration

Thanks for taking time to review the patch!

On 1/13/2023 9:47 PM, Robert Marko wrote:
> 
> On 13. 01. 2023. 16:20, Konrad Dybcio wrote:
>>
>> On 13.01.2023 15:36, devi priya wrote:
>>> Included CLK_IS_CRITICAL flag which helps to properly enable
>>> the APSS PLL during bootup.
>> Please describe the issue and not only the user-visible impact it
>> makes. Does the PLL get shut down by clk_ignore_unused? Maybe you
>> would be interested in the sync_state changes that landed in recent
>> -next that may solve it for you?
>>
>> I don't think it should be always-on, as you have an alternate source
>> for low power modes, adding CLK_IS_CRITICAL will keep the PLL enabled
>> even if you're not using it.
> 
> I have the same opinion, as this is working fine on IPQ6018 and IPQ8074
> and I have not experienced any issues with it.
> 
Sure, will drop the critical flag
>>
>>> clk_rcg2_ops should be used for APSS clock RCG, as other ops
>>> will not configure the RCG register
>> RCG register meaning RCG register*s*, meaning in this case M/N/D
>> which would be required for proper rate setting and not only input
>> switching (which arguably doesn't seem to be of much concern on a
>> single-parent clock)? This all is not obvious..
> Same question from me as well, why do you need clk_rcg2_ops with
> a dummy frequency table since this is just a mux using RCG2 control
> bits?
> 
> Regards,
> Robert
>>
The RCGR is used for source selection whereas the rate setting is done 
by configuring the PLL. The source is configured in the RCGR using the 
source entry (P_APSS_PLL_EARLY) added to the frequency table.

>> Konrad
>>> Co-developed-by: Praveenkumar I <quic_ipkumar@...cinc.com>
>>> Signed-off-by: Praveenkumar I <quic_ipkumar@...cinc.com>
>>> Signed-off-by: devi priya <quic_devipriy@...cinc.com>
>>> ---
>>>   drivers/clk/qcom/apss-ipq-pll.c | 1 +
>>>   drivers/clk/qcom/apss-ipq6018.c | 8 +++++++-
>>>   2 files changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/clk/qcom/apss-ipq-pll.c 
>>> b/drivers/clk/qcom/apss-ipq-pll.c
>>> index dd0c01bf5a98..75486a124fcd 100644
>>> --- a/drivers/clk/qcom/apss-ipq-pll.c
>>> +++ b/drivers/clk/qcom/apss-ipq-pll.c
>>> @@ -33,6 +33,7 @@ static struct clk_alpha_pll ipq_pll = {
>>>               },
>>>               .num_parents = 1,
>>>               .ops = &clk_alpha_pll_huayra_ops,
>>> +            .flags = CLK_IS_CRITICAL,
>>>           },
>>>       },
>>>   };
>>> diff --git a/drivers/clk/qcom/apss-ipq6018.c 
>>> b/drivers/clk/qcom/apss-ipq6018.c
>>> index f2f502e2d5a4..0d0e7196a4dc 100644
>>> --- a/drivers/clk/qcom/apss-ipq6018.c
>>> +++ b/drivers/clk/qcom/apss-ipq6018.c
>>> @@ -33,15 +33,21 @@ static const struct parent_map 
>>> parents_apcs_alias0_clk_src_map[] = {
>>>       { P_APSS_PLL_EARLY, 5 },
>>>   };
>>> +static const struct freq_tbl ftbl_apcs_alias0_clk_src[] = {
>>> +    { .src = P_APSS_PLL_EARLY, .pre_div = 1 },
>>> +    { }
>>> +};
>>> +
>>>   static struct clk_rcg2 apcs_alias0_clk_src = {
>>>       .cmd_rcgr = 0x0050,
>>> +    .freq_tbl = ftbl_apcs_alias0_clk_src,
>>>       .hid_width = 5,
>>>       .parent_map = parents_apcs_alias0_clk_src_map,
>>>       .clkr.hw.init = &(struct clk_init_data){
>>>           .name = "apcs_alias0_clk_src",
>>>           .parent_data = parents_apcs_alias0_clk_src,
>>>           .num_parents = ARRAY_SIZE(parents_apcs_alias0_clk_src),
>>> -        .ops = &clk_rcg2_mux_closest_ops,
>>> +        .ops = &clk_rcg2_ops,
>>>           .flags = CLK_SET_RATE_PARENT,
>>>       },
>>>   };
>>
Best Regards,
Devi Priya