Re: [PATCH 4/8] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Alex Elder <elder@linaro.org>
Cc: arnd@arndb.de, subashab@codeaurora.org, david.brown@linaro.org,
	agross@kernel.org, davem@davemloft.net,
	ilias.apalodimas@linaro.org, cpratapa@codeaurora.org,
	syadagir@codeaurora.org, evgreen@chromium.org,
	benchan@google.com, ejcaruso@google.com, netdev@vger.kernel.org,
	linux-arm-msm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/8] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header
Date: Mon, 20 May 2019 08:49:26 -0700	[thread overview]
Message-ID: <20190520154926.GS2085@tuxbook-pro> (raw)
In-Reply-To: <20190520135354.18628-5-elder@linaro.org>

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

> Replace the use of C bit-fields in the rmnet_map_ul_csum_header
> structure with a single integral structure member, and use field
> masks to encode or get values within that member.
> 
> Note that the previous C bit-fields were defined with CPU local
> endianness.  Their values were computed and then forecfully converted
> to network byte order in rmnet_map_ipv4_ul_csum_header().  Simplify
> that function, and properly define the new csum_info member as a big
> endian value.
> 
> Make similar simplifications in rmnet_map_ipv6_ul_csum_header().
> 

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

> Signed-off-by: Alex Elder <elder@linaro.org>
> ---
>  .../net/ethernet/qualcomm/rmnet/rmnet_map.h   |  9 ++--
>  .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 50 ++++++++-----------
>  2 files changed, 26 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> index a56209645c81..f3231c26badd 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> @@ -60,11 +60,14 @@ struct rmnet_map_dl_csum_trailer {
>  
>  struct rmnet_map_ul_csum_header {
>  	__be16 csum_start_offset;
> -	u16 csum_insert_offset:14;
> -	u16 udp_ip4_ind:1;
> -	u16 csum_enabled:1;
> +	__be16 csum_info;	/* RMNET_MAP_UL_* */
>  } __aligned(1);
>  
> +/* NOTE:  These field masks are defined in CPU byte order */
> +#define RMNET_MAP_UL_CSUM_INSERT_FMASK	GENMASK(13, 0)
> +#define RMNET_MAP_UL_CSUM_UDP_FMASK	GENMASK(14, 14)   /* 0: IP; 1: UDP */
> +#define RMNET_MAP_UL_CSUM_ENABLED_FMASK	GENMASK(15, 15)
> +
>  #define RMNET_MAP_COMMAND_REQUEST     0
>  #define RMNET_MAP_COMMAND_ACK         1
>  #define RMNET_MAP_COMMAND_UNSUPPORTED 2
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 10d2d582a9ce..72b64114505a 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -207,22 +207,18 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,
>  			      struct rmnet_map_ul_csum_header *ul_header,
>  			      struct sk_buff *skb)
>  {
> -	struct iphdr *ip4h = (struct iphdr *)iphdr;
> -	__be16 *hdr = (__be16 *)ul_header, offset;
> +	struct iphdr *ip4h = iphdr;
> +	u16 offset;
> +	u16 val;
>  
> -	offset = htons((__force u16)(skb_transport_header(skb) -
> -				     (unsigned char *)iphdr));
> -	ul_header->csum_start_offset = offset;
> -	ul_header->csum_insert_offset = skb->csum_offset;
> -	ul_header->csum_enabled = 1;
> +	offset = skb_transport_header(skb) - (unsigned char *)iphdr;
> +	ul_header->csum_start_offset = htons(offset);
> +
> +	val = u16_encode_bits(skb->csum_offset, RMNET_MAP_UL_CSUM_INSERT_FMASK);
> +	val |= RMNET_MAP_UL_CSUM_ENABLED_FMASK;
>  	if (ip4h->protocol == IPPROTO_UDP)
> -		ul_header->udp_ip4_ind = 1;
> -	else
> -		ul_header->udp_ip4_ind = 0;
> -
> -	/* Changing remaining fields to network order */
> -	hdr++;
> -	*hdr = htons((__force u16)*hdr);
> +		val |= RMNET_MAP_UL_CSUM_UDP_FMASK;
> +	ul_header->csum_info = htons(val);
>  
>  	skb->ip_summed = CHECKSUM_NONE;
>  
> @@ -249,18 +245,16 @@ rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
>  			      struct rmnet_map_ul_csum_header *ul_header,
>  			      struct sk_buff *skb)
>  {
> -	__be16 *hdr = (__be16 *)ul_header, offset;
> +	u16 offset;
> +	u16 val;
>  
> -	offset = htons((__force u16)(skb_transport_header(skb) -
> -				     (unsigned char *)ip6hdr));
> -	ul_header->csum_start_offset = offset;
> -	ul_header->csum_insert_offset = skb->csum_offset;
> -	ul_header->csum_enabled = 1;
> -	ul_header->udp_ip4_ind = 0;
> +	offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
> +	ul_header->csum_start_offset = htons(offset);
>  
> -	/* Changing remaining fields to network order */
> -	hdr++;
> -	*hdr = htons((__force u16)*hdr);
> +	val = u16_encode_bits(skb->csum_offset, RMNET_MAP_UL_CSUM_INSERT_FMASK);
> +	val |= RMNET_MAP_UL_CSUM_ENABLED_FMASK;
> +	/* Not UDP, so that field is 0 */
> +	ul_header->csum_info = htons(val);
>  
>  	skb->ip_summed = CHECKSUM_NONE;
>  
> @@ -400,8 +394,7 @@ void rmnet_map_checksum_uplink_packet(struct sk_buff *skb,
>  	struct rmnet_map_ul_csum_header *ul_header;
>  	void *iphdr;
>  
> -	ul_header = (struct rmnet_map_ul_csum_header *)
> -		    skb_push(skb, sizeof(struct rmnet_map_ul_csum_header));
> +	ul_header = skb_push(skb, sizeof(*ul_header));
>  
>  	if (unlikely(!(orig_dev->features &
>  		     (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM))))
> @@ -428,10 +421,7 @@ void rmnet_map_checksum_uplink_packet(struct sk_buff *skb,
>  	}
>  
>  sw_csum:
> -	ul_header->csum_start_offset = 0;
> -	ul_header->csum_insert_offset = 0;
> -	ul_header->csum_enabled = 0;
> -	ul_header->udp_ip4_ind = 0;
> +	memset(ul_header, 0, sizeof(*ul_header));
>  
>  	priv->stats.csum_sw++;
>  }
> -- 
> 2.20.1
> 