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

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Message-ID: <1j7c10jmbp.fsf@starbuckisacylon.baylibre.com>
Date: Wed, 25 Jun 2025 09:46:02 +0200
From: Jerome Brunet <jbrunet@...libre.com>
To: Jian Hu <jian.hu@...ogic.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 Wed 25 Jun 2025 at 10:52, Jian Hu <jian.hu@...ogic.com> wrote:

> 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.
>

CLK_DIVIDER_MAX_AT_ZERO maybe ?

> 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.

-- 
Jerome