linux-kernel - Re: [PATCH] clk: Reorder fields in 'struct clk_fractional

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Date:   Sun, 2 Apr 2023 10:22:59 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH] clk: Reorder fields in 'struct clk_fractional_divider'

Le 29/03/2023 à 20:46, Stephen Boyd a écrit :
> Quoting Christophe JAILLET (2023-02-17 07:55:55)
>> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
>> index cf1adfeaf257..8cec844f5dde 100644
>> --- a/include/linux/clk-provider.h
>> +++ b/include/linux/clk-provider.h
>> @@ -1134,13 +1134,13 @@ struct clk_hw *clk_hw_register_fixed_factor_parent_hw(struct device *dev,
>>   struct clk_fractional_divider {
>>          struct clk_hw   hw;
>>          void __iomem    *reg;
>> +       u8              flags;
>>          u8              mshift;
>>          u8              mwidth;
>>          u32             mmask;
> 
> This member ...
> 
>>          u8              nshift;
>>          u8              nwidth;
>>          u32             nmask;
> 
> and this member can be calculated. Doing that would save more bytes when
> combined with this patch. Can you make this into a patch series?

Hi,

with your proposed change, there is no more need to move flags. All u8 
are grouped and the struct is optimal.

I'll send a v2, but not sure it really worth it.
When dynamically allocated, even when the struct is 56 bytes, 64 are 
still allocated.
And there are only 2 users of struct clk_fractional_divider embedded in 
another struct that will be shrinked with your change.

On the other side, having theses masks pre-computed could save a few 
cycles, at nearly no memory usage impact.

I'll let you decide if v1 or v2 is the preferred way to go.

CJ

> 
>> -       u8              flags;
>>          void            (*approximation)(struct clk_hw *hw,
>>                                  unsigned long rate, unsigned long *parent_rate,
>>                                  unsigned long *m, unsigned long *n);
>