linux-kernel - RE: [PATCH net-next v2 5/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum trailer

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Message-ID: <a2954816677f4ae1b27e4cb8e38da0a1@AcuMS.aculab.com>
Date:   Mon, 8 Mar 2021 13:53:05 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alex Elder' <elder@...aro.org>,
        "subashab@...eaurora.org" <subashab@...eaurora.org>,
        "stranche@...eaurora.org" <stranche@...eaurora.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>
CC:     "sharathv@...eaurora.org" <sharathv@...eaurora.org>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "evgreen@...omium.org" <evgreen@...omium.org>,
        "cpratapa@...eaurora.org" <cpratapa@...eaurora.org>,
        "elder@...nel.org" <elder@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next v2 5/6] net: qualcomm: rmnet: don't use C
 bit-fields in rmnet checksum trailer

...
> >> -	if (!csum_trailer->valid) {
> >> +	if (!u8_get_bits(csum_trailer->flags, MAP_CSUM_DL_VALID_FMASK)) {
> >
> > Is that just an overcomplicated way of saying:
> > 	if (!(csum_trailer->flags & MAP_CSUM_DL_VALID_FMASK)) {
> 
> Yes it is.  I defined and used all the field masks in a
> consistent way, but I do think it will read better the
> way you suggest.  Bjorn also asked me privately whether
> GENMASK(15, 15) was just the same as BIT(15) (it is).
> 
> I will post version 3 of the series, identifying which
> fields are single bit/Boolean.  For those I will define
> the value using BIT() and will set/extract using simple
> AND/OR operators.  I won't use the _FMASK suffix on such
> fields.

Even for the checksum offset a simple 'offset << CONSTANT'
is enough.
If it is the bottom bits then even that isn't really needed.
You might want to mask off high bits - but that is an error
path that needs to have been checked earlier.

	David

-
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