Date:   Mon, 18 Feb 2019 15:25:28 +0100
From:   Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
To:     Stanislaw Gruszka <sgruszka@redhat.com>
Cc:     Stefan Wahren <stefan.wahren@i2se.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Felix Fietkau <nbd@nbd.name>,
        Doug Anderson <dianders@chromium.org>,
        Minas Harutyunyan <hminas@synopsys.com>,
        USB list <linux-usb@vger.kernel.org>,
        linux-wireless <linux-wireless@vger.kernel.org>
Subject: Re: [BUG] mt76x0u: Probing issues on Raspberry Pi 3 B+
Message-ID: <20190218142527.GA9283@localhost.localdomain>
References: <CAJ0CqmVFVBXi5E07-ZsYojC7mP4ogpwbcDkDTeebHwX+ayz2DQ@mail.gmail.com>
 <20190212093035.GB12906@redhat.com>
 <404607590.373282.1550126997144@email.ionos.de>
 <20190214092530.GA17273@redhat.com>
 <878a7160-2e91-d057-6d27-c6b9d85f700e@i2se.com>
 <20190215071226.GA2372@redhat.com>
 <1411983628.668277.1550315118443@email.ionos.de>
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> commit 0d9813319b40399a0d8fd761d2fcfedee5701487
> Author: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> Date:   Fri Sep 7 23:13:12 2018 +0200

[...]

> diff --git a/drivers/net/wireless/mediatek/mt76/mt76x02_util.c b/drivers/net/wireless/mediatek/mt76/mt76x02_util.c
> index 062614ad0d51..08425b1d2c30 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76x02_util.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt76x02_util.c
> @@ -550,21 +550,33 @@ void mt76x02_sta_rate_tbl_update(struct ieee80211_hw *hw,
>  }
>  EXPORT_SYMBOL_GPL(mt76x02_sta_rate_tbl_update);
>  
> -int mt76x02_insert_hdr_pad(struct sk_buff *skb)
> +void mt76x02_align_skb(struct sk_buff *skb)
>  {
> -	int len = ieee80211_get_hdrlen_from_skb(skb);
> +	int align = ((unsigned long) skb->data) & 3;
> +	int hdrlen, skblen;
>  
> -	if (len % 4 == 0)
> -		return 0;
> +	hdrlen = ieee80211_get_hdrlen_from_skb(skb);
> +	WARN_ON_ONCE(align == 0 && (hdrlen & 3));
> +
> +	if (align == 0)
> +		return;

Hi Stanislaw,

is it possible that skb->data is 4 byte aligned but hdrlen is not? (e.g 4addr
data frames, not qos)?

>  
> -	skb_push(skb, 2);
> -	memmove(skb->data, skb->data + 2, len);
> +	if (hdrlen & 3) {
> +		/* Align frame and add 2 bytes pad after header. */
> +		skb_push(skb, 2);
> +		memmove(skb->data, skb->data + 2, hdrlen);
>  
> -	skb->data[len] = 0;
> -	skb->data[len + 1] = 0;
> -	return 2;
> +		skb->data[hdrlen] = 0;
> +		skb->data[hdrlen + 1] = 0;
> +	} else {
> +		/* Only for probe request frames. */

are you sure this is true *only* for probe requests?
this could hit performances and it is used even in pci code

Regards,
Lorenzo

> +		skblen = skb->len;
> +		skb_push(skb, 2);
> +		memmove(skb->data, skb->data + 2, skblen);
> +		skb_trim(skb, skblen);
> +	}
>  }
> -EXPORT_SYMBOL_GPL(mt76x02_insert_hdr_pad);
> +EXPORT_SYMBOL_GPL(mt76x02_align_skb);
>  
>  void mt76x02_remove_hdr_pad(struct sk_buff *skb, int len)
>  {
> -- 
> 2.7.5
>