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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Date:   Mon, 8 Mar 2021 10:13:56 +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

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@...aro.org>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>  .../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)) {

    David

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