[PATCH RFT v2 4/5] i3c: mipi-i3c-hci: use get_parity8 helper instead of open coding it
Wolfram Sang
wsa+renesas at sang-engineering.com
Fri Jan 3 02:02:30 PST 2025
> > > > - (dynaddr_parity(address) ? DAT_0_DYNADDR_PARITY : 0);
> > > > + (parity8(address) ? 0 : DAT_0_DYNADDR_PARITY);
...
> The old code is:
> > -static inline bool dynaddr_parity(unsigned int addr)
> > -{
> > - addr |= 1 << 7;
> > - addr += addr >> 4;
> > - addr += addr >> 2;
> > - addr += addr >> 1;
> > - return (addr & 1);
> > -}
>
> So:
> 1) it always sets 0x80.
Right, this is why the arguments of the ternary operator above are
exchanged. The old function was basically 'is_odd'.
> 2) it uses addition not exclusive or.
True, but it will work nonetheless because we are only interested in bit
0 of the result. For one bit, XOR and addition are interchangable. The
overflow to other bits is not important.
> So just not the same definition of 'parity'.
I think it is. I mean, I3C wants odd parity, otherwise it will not work.
And Jarkko kindly confirmed it still works.
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