linux-kernel - Re: [PATCH 5/8] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum trailer

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Message-ID: <20190520171715.GT2085@tuxbook-pro>
Date:   Mon, 20 May 2019 10:17:15 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Alex Elder <elder@...aro.org>
Cc:     arnd@...db.de, subashab@...eaurora.org, david.brown@...aro.org,
        agross@...nel.org, davem@...emloft.net,
        ilias.apalodimas@...aro.org, cpratapa@...eaurora.org,
        syadagir@...eaurora.org, evgreen@...omium.org, benchan@...gle.com,
        ejcaruso@...gle.com, netdev@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] net: qualcomm: rmnet: don't use C bit-fields in
 rmnet checksum trailer

On Mon 20 May 06:53 PDT 2019, Alex Elder wrote:

> Replace the use of C bit-fields in the rmnet_map_dl_csum_trailer
> structure with a single integral field, using field masks to
> encode or get at sub-field values.
> 
> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
>  drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h      | 6 ++++--
>  drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c | 2 +-
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> index f3231c26badd..fb1cdb4ec41f 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> @@ -51,13 +51,15 @@ struct rmnet_map_header {
>  
>  struct rmnet_map_dl_csum_trailer {
>  	u8  reserved1;
> -	u8  valid:1;
> -	u8  reserved2:7;
> +	u8  flags;		/* RMNET_MAP_DL_* */
>  	u16 csum_start_offset;
>  	u16 csum_length;
>  	__be16 csum_value;
>  } __aligned(1);
>  
> +#define RMNET_MAP_DL_CSUM_VALID_FMASK	GENMASK(0, 0)
> +#define RMNET_MAP_DL_RESERVED_FMASK	GENMASK(7, 1)

I presume that the reserved define won't ever be referenced, but it's
good to have it "documented".

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

Regards,
Bjorn

> +
>  struct rmnet_map_ul_csum_header {
>  	__be16 csum_start_offset;
>  	__be16 csum_info;	/* RMNET_MAP_UL_* */
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 72b64114505a..a95111cdcd29 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -362,7 +362,7 @@ 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, RMNET_MAP_DL_CSUM_VALID_FMASK)) {
>  		priv->stats.csum_valid_unset++;
>  		return -EINVAL;
>  	}
> -- 
> 2.20.1
>