Re: [PATCH] mt76: fix frag length allocation for usb

[Stanislaw Gruszka <sgruszka@redhat.com>]

On Wed, Oct 03, 2018 at 11:12:07AM +0200, Lorenzo Bianconi wrote:
> > This is correct fix for c12128ce44b0 ("mt76: use a per rx queue page
> > fragment cache"). We use wrong length when we allocate segments for
> > MCU transmissions, which require bigger segment size than e->buf_size.
> > 
> > Commit 481bb0432414 ("mt76: usb: make rx page_frag_cache access atomic")
> > partially solved the problem or actually mask it by changing
> > mt76u_mcu_init_rx() and mt76u_alloc_queues() sequence, so e->buf_size
> > become non zero any longer, but still not big enough to handle MCU data.
> 
> Hi Stanislaw,
> 
> I agree that we should use len in page_frag_alloc() instead of q->buf_size, so
> 
> Acked-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
> 
> but reviewing the code I guess the real issue is not q->buf_size (since it should
> be bigger than MCU_RESP_URB_SIZE) but it is the sequence of calls in

I added printk and there are allocations where len is bigger then
q->buf_size even with correct mt76u_alloc_queues, mt76u_mcu_init_rx
sequence for mt76x0u:

[16426.606090] q->buf_size 2048 len 2048 nsgs 8sglen 1728
[16426.606131] q->buf_size 2048 len 2048 nsgs 8sglen 1728
[16426.606134] q->buf_size 2048 len 2048 nsgs 8sglen 1728
<snip>
[16426.606464] q->buf_size 2048 len 2048 nsgs 8sglen 1728
[16426.607517] q->buf_size 2048 len 1024 nsgs 1sglen 1024
[16426.939268] q->buf_size 2048 len 14584 nsgs 1sglen 14584
[16426.984955] q->buf_size 2048 len 14584 nsgs 1sglen 14584

Not sure where it come from, but it's after MCU init (which is 1024
third line from end).

> mt76x0u_register_device() since mt76u_alloc_queues need to be called before
> mt76u_mcu_init_rx()

Ok, so this was already fixed in 

commit 481bb0432414f790066205fe77226b7d1877385d
Author: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Date:   Wed Sep 26 13:07:39 2018 +0200

    mt76: usb: make rx page_frag_cache access atomic

but then the sequence was changed again in

commit faa605bdfaa1322ea8e85791abdb3382a8cb4e0c
Author: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Date:   Fri Sep 28 13:39:00 2018 +0200

    mt76x0: usb: move initialization code in usb.c

Thanks
Stanislaw