linux-kernel - Re: [PATCH v3 4/6] clk: meson: t7: add support for the T7 SoC PLL clock

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Message-ID: <22a24fe6-9e62-4aba-825e-aee214f683ee@amlogic.com>
Date: Wed, 25 Jun 2025 10:52:28 +0800
From: Jian Hu <jian.hu@...ogic.com>
To: Jerome Brunet <jbrunet@...libre.com>
Cc: Xianwei Zhao <xianwei.zhao@...ogic.com>, Chuan Liu
 <chuan.liu@...ogic.com>, Neil Armstrong <neil.armstrong@...aro.org>,
 Kevin Hilman <khilman@...libre.com>, Stephen Boyd <sboyd@...nel.org>,
 Michael Turquette <mturquette@...libre.com>,
 Dmitry Rokosov <ddrokosov@...rdevices.ru>, robh+dt <robh+dt@...nel.org>,
 Rob Herring <robh@...nel.org>, devicetree <devicetree@...r.kernel.org>,
 linux-clk <linux-clk@...r.kernel.org>,
 linux-amlogic <linux-amlogic@...ts.infradead.org>,
 linux-kernel <linux-kernel@...r.kernel.org>,
 linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 4/6] clk: meson: t7: add support for the T7 SoC PLL
 clock


On 2025/6/17 0:27, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
>
> On Thu 12 Jun 2025 at 21:02, Jian Hu <jian.hu@...ogic.com> wrote:
>
>>>> +
>>>> +static struct clk_regmap t7_pcie_pll_od = {
>>>> +     .data = &(struct clk_regmap_div_data){
>>>> +             .offset = ANACTRL_PCIEPLL_CTRL0,
>>>> +             .shift = 16,
>>>> +             .width = 5,
>>>> +             .flags = CLK_DIVIDER_ONE_BASED |
>>>> +                      CLK_DIVIDER_ALLOW_ZERO,
>>> What's the behaviour of the divider on zero then ?
>>
>> If there is no CLK_DIVDER_ALLOW_ZERO, there is a warning when registering
>> t7_pcie_pll_od.
>>
>> like this:
>>
>>    ------------[ cut here ]------------
>>    WARNING: CPU: 1 PID: 1 at drivers/clk/clk-divider.c:140
>> divider_recalc_rate+0xfc/0x100
>>    pcie_pll_od: Zero divisor and CLK_DIVIDER_ALLOW_ZERO not set
>>    Modules linked in:
>>   CPU: 1 PID: 1 Comm: swapper/0 Not tainted
>> 5.4.283-09976-ga803e94eed88-dirty #91
>>    Hardware name: tm2_t962e2_ab311 (DT)
>>   Call trace:
>>    [ffffffc020003750+  64][<ffffffc0100e3e3c>] dump_backtrace+0x0/0x1e4
>>    [ffffffc020003790+  32][<ffffffc0100e4044>] show_stack+0x24/0x34
>>    [ffffffc0200037b0+  96][<ffffffc01130a2e8>] dump_stack+0xbc/0x108
>>   [ffffffc020003810+ 144][<ffffffc01010c484>] __warn+0xf4/0x1b8
>>    [ffffffc0200038a0+  64][<ffffffc01010c5f4>] warn_slowpath_fmt+0xac/0xc8
>>   [ffffffc0200038e0+  64][<ffffffc01061d364>] divider_recalc_rate+0xfc/0x100
>>   [ffffffc020003920+  80][<ffffffc010624e84>]
>> clk_regmap_div_recalc_rate+0x74/0x88
>>    [ffffffc020003970+  96][<ffffffc010616a54>] __clk_register+0x62c/0xb78
>>
>> so add it to avoid the warning.
> That does not really answer my question


Sorry, I did not get you before.

I have set OD to 0.  And measure pcie frequency,  It is 37.5Mhz.

4800Mhz/2/32/2=37.5Mhz, and the OD equal zero means divided by 32 in fact.

Here is the test result:

devm 0xfe008140 32

0xD40C04C8

cat /sys/kernel/debug/meson-clk-msr/measure_summary | grep pcie

[16] pcie_clk_inp      37500000  +/1 3125HZ


the OD divider is N crossover. it is one based.

and It's possible to go from 1 to 31 crossovers.