netdev - Re: [PATCH wireless-drivers 2/2] mt76: dma: fix buffer unmap with non-linear skbs

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Date:   Thu, 24 Oct 2019 11:01:48 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Stanislaw Gruszka <sgruszka@...hat.com>
Cc:     kvalo@...eaurora.org, linux-wireless@...r.kernel.org, nbd@....name,
        lorenzo.bianconi@...hat.com, oleksandr@...alenko.name,
        netdev@...r.kernel.org
Subject: Re: [PATCH wireless-drivers 2/2] mt76: dma: fix buffer unmap with
 non-linear skbs

> On Thu, Oct 24, 2019 at 12:23:16AM +0200, Lorenzo Bianconi wrote:
> > mt76 dma layer is supposed to unmap skb data buffers while keep txwi
> > mapped on hw dma ring. At the moment mt76 wrongly unmap txwi or does
> > not unmap data fragments in even positions for non-linear skbs. This
> > issue may result in hw hangs with A-MSDU if the system relies on IOMMU
> > or SWIOTLB. Fix this behaviour properly unmapping data fragments on
> > non-linear skbs.
> 
> If we have to keep txwi mapped, before unmap fragments, when then
> txwi is unmaped ?

txwi are mapped when they are crated in mt76_alloc_txwi(). Whenever we need to
modify them we sync the DMA in mt76_dma_tx_queue_skb(). txwi are unmapped in
mt76_tx_free() at driver unload.

Regards,
Lorenzo

> 
> Stanislaw
> 
> > Fixes: 17f1de56df05 ("mt76: add common code shared between multiple chipsets")
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > ---
> >  drivers/net/wireless/mediatek/mt76/dma.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/wireless/mediatek/mt76/dma.c b/drivers/net/wireless/mediatek/mt76/dma.c
> > index c747eb24581c..8c27956875e7 100644
> > --- a/drivers/net/wireless/mediatek/mt76/dma.c
> > +++ b/drivers/net/wireless/mediatek/mt76/dma.c
> > @@ -93,11 +93,14 @@ static void
> >  mt76_dma_tx_cleanup_idx(struct mt76_dev *dev, struct mt76_queue *q, int idx,
> >  			struct mt76_queue_entry *prev_e)
> >  {
> > -	struct mt76_queue_entry *e = &q->entry[idx];
> >  	__le32 __ctrl = READ_ONCE(q->desc[idx].ctrl);
> > +	struct mt76_queue_entry *e = &q->entry[idx];
> >  	u32 ctrl = le32_to_cpu(__ctrl);
> > +	bool mcu = e->skb && !e->txwi;
> > +	bool first = e->skb == DMA_DUMMY_DATA || e->txwi == DMA_DUMMY_DATA ||
> > +		     (e->skb && !skb_is_nonlinear(e->skb));
> >  
> > -	if (!e->txwi || !e->skb) {
> > +	if (!first || mcu) {
> >  		__le32 addr = READ_ONCE(q->desc[idx].buf0);
> >  		u32 len = FIELD_GET(MT_DMA_CTL_SD_LEN0, ctrl);
> >  
> > @@ -105,7 +108,8 @@ mt76_dma_tx_cleanup_idx(struct mt76_dev *dev, struct mt76_queue *q, int idx,
> >  				 DMA_TO_DEVICE);
> >  	}
> >  
> > -	if (!(ctrl & MT_DMA_CTL_LAST_SEC0)) {
> > +	if (!(ctrl & MT_DMA_CTL_LAST_SEC0) ||
> > +	    e->txwi == DMA_DUMMY_DATA) {
> >  		__le32 addr = READ_ONCE(q->desc[idx].buf1);
> >  		u32 len = FIELD_GET(MT_DMA_CTL_SD_LEN1, ctrl);
> >  
> > -- 
> > 2.21.0
> > 
> 

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