netdev - Re: [PATCH 02/17] bitops: Add generic parity calculation for u64

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Message-ID: <Z8Civv0QaBzmFPTq@thinkpad>
Date: Thu, 27 Feb 2025 12:37:02 -0500
From: Yury Norov <yury.norov@...il.com>
To: Jiri Slaby <jirislaby@...nel.org>
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	Yu-Chun Lin <eleanor15x@...il.com>
Subject: Re: [PATCH 02/17] bitops: Add generic parity calculation for u64

On Thu, Feb 27, 2025 at 07:38:58AM +0100, Jiri Slaby wrote:
> On 26. 02. 25, 19:33, Yury Norov wrote:
> > > Not in cases where macros are inevitable. I mean, do we need parityXX() for
> > > XX in (8, 16, 32, 64) at all? Isn't the parity() above enough for everybody?
> > 
> > The existing codebase has something like:
> > 
> >          int ret;
> > 
> >          ret = i3c_master_get_free_addr(m, last_addr + 1);
> >          ret |= parity8(ret) ? 0 : BIT(7)
> > 
> > So if we'll switch it to a macro like one above, it will become a
> > 32-bit parity. It wouldn't be an error because i3c_master_get_free_addr()
> > returns an u8 or -ENOMEM, and the error code is checked explicitly.
> > 
> > But if we decide to go with parity() only, some users will have to
> > call it like parity((u8)val) explicitly. Which is not bad actually.
> 
> That cast looks ugly -- we apparently need parityXX(). (In this particular
> case we could do parity8(last_addr), but I assume there are more cases like
> this.) Thanks for looking up the case for this.

This parity8() is used in just 2 drivers - i3c and hwmon/spd5118. The hwmon
driver looks good. I3C, yeah, makes this implied typecast, which is nasty
regardless.

This is the new code, and I think if we all agree that generic parity()
would be a better API, it's a good time to convert existing users now.

Thanks,
Yury