linux-kernel - Re: [PATCH v1 1/1] clk: fractional-divider: Move mask calculations out of lock

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Date: Sat, 9 Mar 2024 08:19:57 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Andy Shevchenko <andy.shevchenko@...il.com>, linux-clk@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Michael Turquette <mturquette@...libre.com>,
 Stephen Boyd <sboyd@...nel.org>, Heiko Stuebner <heiko@...ech.de>
Subject: Re: [PATCH v1 1/1] clk: fractional-divider: Move mask calculations
 out of lock

Le 03/03/2024 à 13:14, Andy Shevchenko a écrit :
> There is no need to calculate masks under the lock taken.
> Move them out of it.
> 
> Signed-off-by: Andy Shevchenko <andy.shevchenko@...il.com>
> ---
>   drivers/clk/clk-fractional-divider.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
> index a0178182fc72..da057172cc90 100644
> --- a/drivers/clk/clk-fractional-divider.c
> +++ b/drivers/clk/clk-fractional-divider.c
> @@ -195,14 +195,14 @@ static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
>   		n--;
>   	}
>   
> +	mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
> +	nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
> +

Hi,

if this is a hot path, you could maybe even compute:
    mask = ~(GENMASK(fd->mwidth - 1, 0) << fd->mshift |
             GENMASK(fd->nwidth - 1, 0) << fd->nshift)

unless gcc is smart enough to do it by itself.

>   	if (fd->lock)
>   		spin_lock_irqsave(fd->lock, flags);
>   	else
>   		__acquire(fd->lock);
>   
> -	mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
> -	nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
> -
>   	val = clk_fd_readl(fd);
>   	val &= ~(mmask | nmask);

    val &= mask;

>   	val |= (m << fd->mshift) | (n << fd->nshift);

and pre-compute "(m << fd->mshift) | (n << fd->nshift)" outside of the 
lock too.

CJ