linux-kernel - Re: [PATCH v2 3/5] clk: amlogic: Add handling for PLL lock failure

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Message-ID: <4f245c6a-5a03-4321-bbf8-61249a7a550f@amlogic.com>
Date: Thu, 30 Oct 2025 17:15:22 +0800
From: Chuan Liu <chuan.liu@...ogic.com>
To: Jerome Brunet <jbrunet@...libre.com>,
 Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@...nel.org>
Cc: Neil Armstrong <neil.armstrong@...aro.org>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Kevin Hilman <khilman@...libre.com>,
 Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
 linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 da@...re.computer
Subject: Re: [PATCH v2 3/5] clk: amlogic: Add handling for PLL lock failure

Hi Jerome,

On 10/30/2025 4:32 PM, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
> 
> On Thu 30 Oct 2025 at 13:24, Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@...nel.org> wrote:
> 
>> From: Chuan Liu <chuan.liu@...ogic.com>
>>
>> If the PLL fails to lock, it should be disabled, This makes the logic
>> more complete, and also helps save unnecessary power consumption when
>> the PLL is malfunctioning.
>>
>> Signed-off-by: Chuan Liu <chuan.liu@...ogic.com>
>> ---
>>   drivers/clk/meson/clk-pll.c | 41 +++++++++++++++++++++++------------------
>>   1 file changed, 23 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c
>> index f81ebf6cc981..6c794adb8ccd 100644
>> --- a/drivers/clk/meson/clk-pll.c
>> +++ b/drivers/clk/meson/clk-pll.c
>> @@ -353,6 +353,23 @@ static int meson_clk_pcie_pll_enable(struct clk_hw *hw)
>>        return -EIO;
>>   }
>>
>> +static void meson_clk_pll_disable(struct clk_hw *hw)
>> +{
>> +     struct clk_regmap *clk = to_clk_regmap(hw);
>> +     struct meson_clk_pll_data *pll = meson_clk_pll_data(clk);
>> +
>> +     /* Put the pll is in reset */
>> +     if (MESON_PARM_APPLICABLE(&pll->rst))
>> +             meson_parm_write(clk->map, &pll->rst, 1);
>> +
>> +     /* Disable the pll */
>> +     meson_parm_write(clk->map, &pll->en, 0);
>> +
>> +     /* Disable PLL internal self-adaption current module */
>> +     if (MESON_PARM_APPLICABLE(&pll->current_en))
>> +             meson_parm_write(clk->map, &pll->current_en, 0);
>> +}
>> +
>>   static int meson_clk_pll_enable(struct clk_hw *hw)
>>   {
>>        struct clk_regmap *clk = to_clk_regmap(hw);
>> @@ -397,29 +414,17 @@ static int meson_clk_pll_enable(struct clk_hw *hw)
>>                meson_parm_write(clk->map, &pll->l_detect, 0);
>>        }
>>
>> -     if (meson_clk_pll_wait_lock(hw))
>> +     if (meson_clk_pll_wait_lock(hw)) {
>> +             /* disable PLL when PLL lock failed. */
>> +             meson_clk_pll_disable(hw);
>> +             pr_warn("%s: PLL lock failed!!!\n", clk_hw_get_name(hw));
>> +
> 
> This is something that's likely to spam, so pr_warn_once() (if you must warn)
> and I don't think 3 "!" are necessary to convey the message.
> 

In the next version, I'll remove the "!", and replace pr_warn to
pr_warn_once.

Some drivers that reference the clock may not check the function’s
return value (even though that's not ideal), so adding this warning
makes the issue more noticeable.

>>                return -EIO;
>> +     }
>>
>>        return 0;
>>   }
>>
>> -static void meson_clk_pll_disable(struct clk_hw *hw)
>> -{
>> -     struct clk_regmap *clk = to_clk_regmap(hw);
>> -     struct meson_clk_pll_data *pll = meson_clk_pll_data(clk);
>> -
>> -     /* Put the pll is in reset */
>> -     if (MESON_PARM_APPLICABLE(&pll->rst))
>> -             meson_parm_write(clk->map, &pll->rst, 1);
>> -
>> -     /* Disable the pll */
>> -     meson_parm_write(clk->map, &pll->en, 0);
>> -
>> -     /* Disable PLL internal self-adaption current module */
>> -     if (MESON_PARM_APPLICABLE(&pll->current_en))
>> -             meson_parm_write(clk->map, &pll->current_en, 0);
>> -}
>> -
>>   static int meson_clk_pll_set_rate(struct clk_hw *hw, unsigned long rate,
>>                                  unsigned long parent_rate)
>>   {
> 
> --
> Jerome