linux-kernel - Re: [PATCH v2 08/11] clk: qcom: dispcc: Add support for display clock controller Kaanapali

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Message-ID: <8d0ec7fc-6eb0-4b71-8e0f-3deaf1f489d6@oss.qualcomm.com>
Date: Mon, 1 Dec 2025 14:20:44 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Taniya Das <taniya.das@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd
 <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Ajit Pandey <ajit.pandey@....qualcomm.com>,
        Imran Shaik <imran.shaik@....qualcomm.com>,
        Jagadeesh Kona <jagadeesh.kona@....qualcomm.com>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 08/11] clk: qcom: dispcc: Add support for display clock
 controller Kaanapali

On 11/26/25 1:09 AM, Dmitry Baryshkov wrote:
> On Tue, Nov 25, 2025 at 11:15:17PM +0530, Taniya Das wrote:
>> Support the clock controller driver for Kaanapali to enable display SW to
>> be able to control the clocks.
>>
>> Signed-off-by: Taniya Das <taniya.das@....qualcomm.com>
>> ---

[...]

>> +/* 257.142858 MHz Configuration */
> 
> This is a bit strange frequency for the boot config.

The frequency map lists this odd cookie as the lowest predefined config,
perhaps it was pulled from there.

More interestingly, the only consumer of this PLL (MDP_CLK_SRC) makes no
effort to use the m/n/d registers, instead relying on the PLL to re-clock
for its ratesetting with a fixed divider of 3 (and div1 @ XO rate).

257.142858 * 3 = 771.428574 over-drives MDP_CLK_SRC, FWIW.

Taniya, we've seen something like this in camera too. Is there a reason
the frequency is being set this way?

Konrad

> 
>> +static const struct alpha_pll_config disp_cc_pll0_config = {
>> +	.l = 0xd,
>> +	.cal_l = 0x48,
>> +	.alpha = 0x6492,
>> +	.config_ctl_val = 0x25c400e7,
>> +	.config_ctl_hi_val = 0x0a8062e0,
>> +	.config_ctl_hi1_val = 0xf51dea20,
>> +	.user_ctl_val = 0x00000008,
>> +	.user_ctl_hi_val = 0x00000002,
>> +};
>> +
>