linux-kernel - Re: [PATCH] clk: qcom: clk-alpha-pll: Replace divide operator with comparison

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Message-ID: <7733a4ca-330b-4127-af12-33f376fbbc47@nvidia.com>
Date: Wed, 28 Aug 2024 14:47:05 +0100
From: Jon Hunter <jonathanh@...dia.com>
To: Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
 Satya Priya Kakitapalli <quic_skakitap@...cinc.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
 linux-kernel@...r.kernel.org, Ajit Pandey <quic_ajipan@...cinc.com>,
 Imran Shaik <quic_imrashai@...cinc.com>, Taniya Das <quic_tdas@...cinc.com>,
 Jagadeesh Kona <quic_jkona@...cinc.com>, kernel test robot <lkp@...el.com>,
 Dan Carpenter <dan.carpenter@...aro.org>,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] clk: qcom: clk-alpha-pll: Replace divide operator with
 comparison

Hi Satya, Vladimir,

On 13/08/2024 21:01, Vladimir Zapolskiy wrote:
> On 8/13/24 12:40, Satya Priya Kakitapalli wrote:
>> In zonda_pll_adjust_l_val() replace the divide operator with comparison
>> operator since comparisons are faster than divisions.
>>
>> Fixes: f4973130d255 ("clk: qcom: clk-alpha-pll: Update set_rate for 
>> Zonda PLL")
> 
> Apparently the change is not a fix, therefore I believe the Fixes tag
> shall be removed.


 From the commit message it is not clear that this is a fix, but I
believe that it is. With the current -next I am seeing the following
build error (with GCC 7.3.1) on ARM ...

drivers/clk/qcom/clk-alpha-pll.o: In function `clk_zonda_pll_set_rate':
clk-alpha-pll.c:(.text+0x45dc): undefined reference to `__aeabi_uldivmod'
  
>> Reported-by: kernel test robot <lkp@...el.com>
>> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
>> Closes: https://lore.kernel.org/r/202408110724.8pqbpDiD-lkp@intel.com/

There is also the above smatch warning that was reported.

>> Signed-off-by: Satya Priya Kakitapalli <quic_skakitap@...cinc.com>
>> ---
>>   drivers/clk/qcom/clk-alpha-pll.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/clk/qcom/clk-alpha-pll.c 
>> b/drivers/clk/qcom/clk-alpha-pll.c
>> index 2f620ccb41cb..fd8a82bb3690 100644
>> --- a/drivers/clk/qcom/clk-alpha-pll.c
>> +++ b/drivers/clk/qcom/clk-alpha-pll.c
>> @@ -2126,7 +2126,7 @@ static void zonda_pll_adjust_l_val(unsigned long 
>> rate, unsigned long prate, u32
>>       remainder = do_div(quotient, prate);
>>       *l = quotient;
> 
> Since it's not a fix, but a simplification, you may wish to remove
> an unnecessary 'quotient' local variable:
> 
> remainder = do_div(rate, prate);
> 
>> -    if ((remainder * 2) / prate)
>> +    if ((remainder * 2) >= prate)
>>           *l = *l + 1;
> 
> *l = rate + (u32)(remainder * 2 >= prate);


The above change does fix this build error for me.

Satya, did you intend this to be a fix? Can we get this into -next?

Thanks
Jon

-- 
nvpublic