linux-kernel - Re: [PATCH] clk: qcom: gcc-qcs404: fix initial rate of GPLL3

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Message-ID: <4c129bca-017c-4123-b9e8-547881b246c8@gmail.com>
Date: Tue, 22 Oct 2024 15:01:56 +0200
From: Gabor Juhos <j4g8y7@...il.com>
To: Bryan O'Donoghue <pure.logic@...us-software.ie>,
 Bjorn Andersson <andersson@...nel.org>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Taniya Das <quic_tdas@...cinc.com>
Cc: Vinod Koul <vkoul@...nel.org>, linux-arm-msm@...r.kernel.org,
 linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH] clk: qcom: gcc-qcs404: fix initial rate of GPLL3

Hi Bryan,

2024. 10. 22. 11:53 keltezéssel, Bryan O'Donoghue írta:
> On 22/10/2024 10:45, Gabor Juhos wrote:
>> The comment before the config of the GPLL3 PLL says that the
>> PLL should run at 930 MHz. In contrary to this, calculating
>> the frequency from the current configuration values by using
>> 19.2 MHz as input frequency defined in 'qcs404.dtsi', it gives
>> 921.6 MHz:
>>
>>    $ xo=19200000; l=48; alpha=0x0; alpha_hi=0x0
>>    $ echo "$xo * ($((l)) + $(((alpha_hi << 32 | alpha) >> 8)) / 2^32)" | bc -l
>>    921600000.00000000000000000000
>>
>> Set 'alpha_hi' in the configuration to a value used in downstream
>> kernels [1][2] in order to get the correct output rate:
>>
>>    $ xo=19200000; l=48; alpha=0x0; alpha_hi=0x70
>>    $ echo "$xo * ($((l)) + $(((alpha_hi << 32 | alpha) >> 8)) / 2^32)" | bc -l
>>    930000000.00000000000000000000
>>
>> The change is based on static code analysis, compile tested only.
>>
>> [1] https://git.codelinaro.org/clo/la/kernel/msm-5.4/-/blob/
>> kernel.lnx.5.4.r56-rel/drivers/clk/qcom/gcc-qcs404.c?ref_type=heads#L335
>> [2} https://git.codelinaro.org/clo/la/kernel/msm-5.15/-/blob/
>> kernel.lnx.5.15.r49-rel/drivers/clk/qcom/gcc-qcs404.c?ref_type=heads#L127
>>
>> Cc: stable@...r.kernel.org
>> Fixes: 652f1813c113 ("clk: qcom: gcc: Add global clock controller driver for
>> QCS404")
>> Signed-off-by: Gabor Juhos <j4g8y7@...il.com>
> It should be possible to test / verify this change with debugcc on qcs404
> 
> https://github.com/linux-msm/debugcc/blob/master/qcs404.c

Thank you for the suggestion. Unfortunately, I have no suitable hardware to test
that.

-Gabor