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

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Message-ID: <b8eee15f-e3e4-4a2d-853e-31e966c19cf5@linaro.org>
Date:   Tue, 31 Jan 2023 11:40:32 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Devi Priya <quic_devipriy@...cinc.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,
        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
Subject: Re: [PATCH 6/6] clk: qcom: Fix APSS PLL and RCG Configuration

On 31/01/2023 11:17, Devi Priya wrote:
> Thanks for taking time to review the patch
> 
> On 1/13/2023 8:50 PM, 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.
> Yeah, got it. 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..
>>
>> Konrad
> The source selection is done by configuring the RCGR config register 
> with the source entry (P_APSS_PLL_EARLY) added to the frequency table. 
> Proper rate is achieved by configuring the PLL and hence M/N/D values 
> are not configured

But the clk_rcg2_mux_closest_ops also programs the parent for the clock. 
So from your description it isn't obvious what is wrong with the current 
_ops used for the clock.

>>>
>>> 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

-- 
With best wishes
Dmitry