Re: [PATCH 2/2] net: macb: Add support for SiFive FU540-C000

From: Palmer Dabbelt
Date: Wed May 29 2019 - 22:46:21 EST


On Fri, 24 May 2019 06:48:47 PDT (-0700), andrew@xxxxxxx wrote:
On Fri, May 24, 2019 at 10:22:06AM +0530, Yash Shah wrote:
On Thu, May 23, 2019 at 8:24 PM Andrew Lunn <andrew@xxxxxxx> wrote:
>
> > +static int fu540_macb_tx_set_rate(struct clk_hw *hw, unsigned long rate,
> > + unsigned long parent_rate)
> > +{
> > + rate = fu540_macb_tx_round_rate(hw, rate, &parent_rate);
> > + iowrite32(rate != 125000000, mgmt->reg);
>
> That looks odd. Writing the result of a comparison to a register?

The idea was to write "1" to the register if the value of rate is
anything else than 125000000.

I'm not a language lawyer. Is it guaranteed that an expression like
this returns 1? Any value !0 is true, so maybe it actually returns 42?

From Stack Overflow: https://stackoverflow.com/questions/18097922/return-value-of-operator-in-c

"C11(ISO/IEC 9899:201x) Â6.5.8 Relational operators

Each of the operators < (less than), > (greater than), <= (less than or equal
to), and >= (greater than or equal to) shall yield 1 if the specified relation
is true and 0 if it is false. The result has type int."

To make it easier to read, I will change this to below:
- iowrite32(rate != 125000000, mgmt->reg);
+ if (rate != 125000000)
+ iowrite32(1, mgmt->reg);
+ else
+ iowrite32(0, mgmt->reg);

Hope that's fine. Thanks for your comment

Yes, that is good.

Andrew