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

[Alex Elder]

On 3/8/21 4:13 AM, David Laight wrote:
> From: Alex Elder
> > Sent: 06 March 2021 03:16
> >
> > Replace the use of C bit-fields in the rmnet_map_dl_csum_trailer
> > structure with a single one-byte field, using constant field masks
> > to encode or get at embedded values.
> >
> > Signed-off-by: Alex Elder <elder@xxxxxxxxxx>
> > Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
> > ---
> >   .../ethernet/qualcomm/rmnet/rmnet_map_data.c    |  2 +-
> >   include/linux/if_rmnet.h                        | 17 +++++++----------
> >   2 files changed, 8 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> > b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> > index 3291f252d81b0..29d485b868a65 100644
> > --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> > +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> > @@ -365,7 +365,7 @@ int rmnet_map_checksum_downlink_packet(struct sk_buff *skb, u16 len)
> >
> >   	csum_trailer = (struct rmnet_map_dl_csum_trailer *)(skb->data + len);
> >
> > -	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.

Thanks a lot for your comment/question/suggestion.  I
like it.

					-Alex

>      David
>
> -
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