linux-kernel - Re: [PATCH] clk:sophgo:clk-cv18xx-pll

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Message-ID: <ryzruhrgh4cygftrtoig4epyzkg3kgqg4ua5rmadvlylyh5oan@5fjaqecknce4>
Date: Wed, 13 Nov 2024 09:16:33 +0800
From: Inochi Amaoto <inochiama@...il.com>
To: Chen Wang <unicorn_wang@...look.com>, 
	Ragavendra <ragavendra.bn@...il.com>, mturquette@...libre.com, sboyd@...nel.org, inochiama@...look.com
Cc: linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk:sophgo:clk-cv18xx-pll

On Wed, Nov 13, 2024 at 08:33:54AM +0800, Chen Wang wrote:
> Pleas improve the patch title and just write "fix..." instead of listing the
> file name changed.
> 
> On 2024/11/13 6:58, Ragavendra wrote:
> > Initializing the val variable of type u32 as it was not initialized.
> > 
> Please add "Fixes" tag here, see
> https://www.kernel.org/doc/html/latest/process/submitting-patches.html.
> > Signed-off-by: Ragavendra Nagraj <ragavendra.bn@...il.com>
> > ---
> >   drivers/clk/sophgo/clk-cv18xx-pll.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/clk/sophgo/clk-cv18xx-pll.c b/drivers/clk/sophgo/clk-cv18xx-pll.c
> > index 29e24098bf5f..04a0419cab4e 100644
> > --- a/drivers/clk/sophgo/clk-cv18xx-pll.c
> > +++ b/drivers/clk/sophgo/clk-cv18xx-pll.c
> > @@ -87,7 +87,7 @@ static int ipll_find_rate(const struct cv1800_clk_pll_limit *limit,
> >   static int ipll_determine_rate(struct clk_hw *hw, struct clk_rate_request *req)
> >   {
> > -	u32 val;
> > +	u32 val = 0;
> >   	struct cv1800_clk_pll *pll = hw_to_cv1800_clk_pll(hw);
> >   	return ipll_find_rate(pll->pll_limit, req->best_parent_rate,
> 
> I looked at ipll_find_rate() and found that the parameters "rate"/"value"
> are both input and output parameters, which is really a place that needs to
> be treated with caution.
> 
> Seems this patch change is correct, otherwise the value of "detected" in the
> function will be random after calling ipll_find_rate here.  Actually I
> suggest adding some comments for ipll_find_rate() to emphasize it.
> Otherwise, it is easy to think that "rate" and "value" are only output
> parameters at first glance.
> 

Since ipll_determine_rate does not use "val" in later,
it is OK to not init it. 

> But I raised a question here: In ipll_find_rate(), do we really need to make
> "detected" depend on the value of external input? Inochi, can you please
> comment on this, due to you are the author of this code.
> 

As using the detected value, an extra mask is used
to emit unused field. See macro PLL_COPY_REG.
A more suitable fix may init the "detected" to 0 in the 
ipll/fpll_find_rate to make "value" is output only.

Regards,
Inochi