linux-kernel - Re: [PATCH v4 1/1] i2c: designware: use casting of u64 in clock multiplication to avoid overflow

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Date:   Tue, 20 Dec 2022 21:23:53 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     "Hawa, Hanna" <hhhawa@...zon.com>
Cc:     wsa@...nel.org, jarkko.nikula@...ux.intel.com,
        mika.westerberg@...ux.intel.com, jsd@...ihalf.com,
        linus.walleij@...aro.org, ben-linux@...ff.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        dwmw@...zon.co.uk, benh@...zon.com, ronenk@...zon.com,
        talel@...zon.com, jonnyc@...zon.com, hanochu@...zon.com,
        farbere@...zon.com, itamark@...zon.com,
        Lareine Khawaly <lareine@...zon.com>
Subject: Re: [PATCH v4 1/1] i2c: designware: use casting of u64 in clock
 multiplication to avoid overflow

On Tue, Dec 20, 2022 at 07:43:06PM +0200, Hawa, Hanna wrote:
> On 12/20/2022 7:11 PM, Andy Shevchenko wrote:
> > On Tue, Dec 20, 2022 at 04:48:06PM +0000, Hanna Hawa wrote:

...

> > > -             return DIV_ROUND_CLOSEST(ic_clk * tSYMBOL, MICRO) - 8 + offset;
> > > +             return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * tSYMBOL, MICRO) - 8 +
> > > +                     offset;
> > 
> > Broken indentation.

...

> > > -             return DIV_ROUND_CLOSEST(ic_clk * (tSYMBOL + tf), MICRO) - 3 + offset;
> > > +             return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * (tSYMBOL + tf),
> > > +                                          MICRO) - 3 + offset;
> > 
> > I would still go with 'MICRO) -' part to be on the previous line despite being
> > over 80, this is logical split which increases readability.
> 
> Okay.. will move the 'MICRO) -' one line before
> > 
> > > -     return DIV_ROUND_CLOSEST(ic_clk * (tLOW + tf), MICRO) - 1 + offset;
> > > +     return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * (tLOW + tf), MICRO) - 1 +
> > > +             offset;
> > 
> > Broken indentation.
> 
> Why it's broken indentation? I'm asking to know for the next time. The word
> 'offset' is not part of DIV_ROUND_CLOSEST_ULL parentheses. In wrong
> indentation the checkpatch shout about it, but it didn't happen with the
> above.

The continuation line of the expression should go under the opening
parentheses, but you are right, the part outside DIV_ should be under
D and not as you suggested below.

But the problem is that you made illogical split while I suggested to leave
DIV_...() on one line and the rest on the other.

> Does the below the correct indentation?

No.

		return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * tSYMBOL, MICRO) -
		       8 + offset;

		return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * (tSYMBOL + tf), MICRO) -
		       3 + offset;

	return DIV_ROUND_CLOSEST_ULL((u64)ic_clk * (tLOW + tf), MICRO) -
	       1 + offset;

-- 
With Best Regards,
Andy Shevchenko