linux-kernel - Re: [PATCH 2/4] clk: qcom: clk-rcg2: Make sure to not write d=0 to the NMD register

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Message-ID: <b55dc8e9ec0e8549fe61e6439a02f912@trvn.ru>
Date:   Sat, 08 Jan 2022 12:29:42 +0500
From:   Nikita Travkin <nikita@...n.ru>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     linus.walleij@...aro.org, mturquette@...libre.com,
        bjorn.andersson@...aro.org, agross@...nel.org, tdas@...eaurora.org,
        svarbanov@...sol.com, linux-arm-msm@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH 2/4] clk: qcom: clk-rcg2: Make sure to not write d=0 to
 the NMD register

Hi,

Stephen Boyd писал(а) 08.01.2022 05:56:
> Quoting Nikita Travkin (2021-12-09 08:37:18)
>> Sometimes calculation of d value may result in 0 because of the
>> rounding after integer division. This causes the following error:
>>
>> [  113.969689] camss_gp1_clk_src: rcg didn't update its configuration.
>> [  113.969754] WARNING: CPU: 3 PID: 35 at drivers/clk/qcom/clk-rcg2.c:122 update_config+0xc8/0xdc
>>
>> Make sure that D value is never zero.
>>
>> Fixes: 7f891faf596e ("clk: qcom: clk-rcg2: Add support for duty-cycle for RCG")
>> Signed-off-by: Nikita Travkin <nikita@...n.ru>
>> ---
>>  drivers/clk/qcom/clk-rcg2.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
>> index 6964cf914b60..fdfd43e2a01b 100644
>> --- a/drivers/clk/qcom/clk-rcg2.c
>> +++ b/drivers/clk/qcom/clk-rcg2.c
>> @@ -424,6 +424,10 @@ static int clk_rcg2_set_duty_cycle(struct clk_hw *hw, struct clk_duty *duty)
>>         if (d > mask)
>>                 d = mask;
>>
>> +       /* Hardware can't handle d=0, make sure it's at least 1 */
>> +       if (!d)
>> +               d = 1;
> 
> Maybe clamp() would be better
> 
> 	/*
>  	 * Check bit widths of 2d. If D is too big reduce duty cycle and
> 	 * ensure it is non-zero.
> 	 */
> 	clamp(d, 1, mask);
> 

Yes, this looks nicer, will use it in v2. Thanks for the suggestion!

Nikita

>> +
>>         if ((d / 2) > (n - m))
>>                 d = (n - m) * 2;
>>         else if ((d / 2) < (m / 2))