On Oct 24, Felix Fietkau wrote:
> On 2019-10-24 00:23, 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.
> >
> > Fixes: 17f1de56df05 ("mt76: add common code shared between multiple chipsets")
> > Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
> > ---
> > 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));
> It seems to me that these conditions could be true not just for the
> first entry, but also following entries except for the last one.
> I think we should add a 'bool has_txwi' field in struct mt76_queue_entry
> to indicate that the first dma address points to a txwi that should not
> be unmapped.
I agree 'first' is misleading since this condition is used to unamp even the
very last data fragment if we have an even number of data fragments
(e.g linear area + one fragment). For the following entries except for the last
one 'first' is false since e->skb is NULL (e->skb is not NULL just for the very
last entry), right? Btw we can remove mcu bool.
In order to improve code readability I agree to add a bool in mt76_queue_entry to
unmap buf0. I will fix it in v2.
Regards,
Lorenzo
>
> - Felix
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