Re: [PATCH v2 2/2] mt76: usb: do not always copy the first part of received frames

[Lorenzo Bianconi <lorenzo.bianconi@redhat.com>]

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> On Fri, May 31, 2019 at 11:38:23AM +0200, Lorenzo Bianconi wrote:

[...]

> >  	}
> >  
> >  	urb->num_sgs = max_t(int, i, urb->num_sgs);
> > -	urb->transfer_buffer_length = urb->num_sgs * q->buf_size,
> > +	urb->transfer_buffer_length = urb->num_sgs * data_size;
> >  	sg_init_marker(urb->sg, urb->num_sgs);
> >  
> >  	return i ? : -ENOMEM;
> > @@ -611,8 +611,12 @@ static int mt76u_alloc_rx(struct mt76_dev *dev)
> >  	if (!q->entry)
> >  		return -ENOMEM;
> >  
> > -	q->buf_size = dev->usb.sg_en ? MT_RX_BUF_SIZE : PAGE_SIZE;
> > +	if (dev->usb.sg_en)
> > +		q->buf_size = MT_BUF_WITH_OVERHEAD(MT_RX_BUF_SIZE);
> 
> I strongly recommend to not doing this. While this should work
> in theory creating buffer with size of 2k + some bytes might
> trigger various bugs in dma mapping or other low level code.

even in practice actually :) but we can be more cautious since probably copying
the first 128B will not make any difference

> 
> And skb_shered_info is needed only in first buffer IIUC.
> 
> Also this patch seems to make first patch unnecessary except for
> non sg_en case (in which I think rx AMSDU is broken anyway),
> so I would prefer just to apply first patch.

I do not think rx AMSDU is broken for non sg_en case since the max rx value
allowed should be 3839 IIRC and we alloc one page in this case

Regards,
Lorenzo

> 
> Stanislaw
> 

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