linux-kernel - Re: [PATCH 1/8] net: qualcomm: rmnet: fix struct rmnet_map

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Date:   Mon, 20 May 2019 08:38:47 -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 1/8] net: qualcomm: rmnet: fix struct rmnet_map_header

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

> The C bit-fields in the first byte of the rmnet_map_header structure
> are defined in the wrong order.  The first byte should be formatted
> this way:
>                  +------- reserved_bit
>                  | +----- cd_bit
>                  | |
>                  v v
>     +-----------+-+-+
>     |  pad_len  |R|C|
>     +-----------+-+-+
>      7 6 5 4 3 2 1 0  <-- bit position
> 
> But the C bit-fields that define the first byte are defined this way:
>     u8 pad_len:6;
>     u8 reserved_bit:1;
>     u8 cd_bit:1;
> 
> And although this isn't portable, I can state that when I build it
> the result puts the bit-fields in the wrong location (e.g., the
> cd_bit is in bit position 7, when it should be position 0).
> 
> Fix this by reordering the definitions of these struct members.
> Upcoming patches will reimplement these definitions portably.
> 

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

Regards,
Bjorn

> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
>  drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> index 884f1f52dcc2..b1ae9499c0b2 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> @@ -40,9 +40,9 @@ enum rmnet_map_commands {
>  };
>  
>  struct rmnet_map_header {
> -	u8  pad_len:6;
> -	u8  reserved_bit:1;
>  	u8  cd_bit:1;
> +	u8  reserved_bit:1;
> +	u8  pad_len:6;
>  	u8  mux_id;
>  	__be16 pkt_len;
>  }  __aligned(1);
> -- 
> 2.20.1
>