Re: [PATCH] mac80211: round IEEE80211_TX_STATUS_HEADROOM up to multiple of 4

[Arend van Spriel <arend.vanspriel@broadcom.com>]

On 2/9/2018 7:51 PM, Felix Fietkau wrote:
> This ensures that mac80211 allocated management frames are properly
> aligned, which makes copying them more efficient.
> For instance, mt76 uses iowrite32_copy to copy beacon frames to beacon
> template memory on the chip.
> Misaligned 32-bit accesses cause CPU exceptions on MIPS and should be
> avoided.
>
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
> ---
>   include/net/mac80211.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/net/mac80211.h b/include/net/mac80211.h
> index 906e90223066..d999b8c8a44b 100644
> --- a/include/net/mac80211.h
> +++ b/include/net/mac80211.h
> @@ -4149,7 +4149,7 @@ void ieee80211_sta_uapsd_trigger(struct ieee80211_sta *sta, u8 tid);
>    * The TX headroom reserved by mac80211 for its own tx_status functions.
>    * This is enough for the radiotap header.

Hi Felix,

Maybe useful to mention the alignment requirement in this comment block.

>    */
> -#define IEEE80211_TX_STATUS_HEADROOM	14
> +#define IEEE80211_TX_STATUS_HEADROOM	16

Regards,
Arend