diff mbox series

[22/28] sgiseeq: convert from dma_cache_sync to dma_sync_single_for_device

Message ID 20200819065555.1802761-23-hch@lst.de
State New
Headers show
Series None | expand

Commit Message

Christoph Hellwig Aug. 19, 2020, 6:55 a.m. UTC
Use the proper modern API to transfer cache ownership for incoherent DMA.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/net/ethernet/seeq/sgiseeq.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Comments

Thomas Bogendoerfer Sept. 1, 2020, 3:22 p.m. UTC | #1
On Wed, Aug 19, 2020 at 08:55:49AM +0200, Christoph Hellwig wrote:
> Use the proper modern API to transfer cache ownership for incoherent DMA.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/net/ethernet/seeq/sgiseeq.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/seeq/sgiseeq.c b/drivers/net/ethernet/seeq/sgiseeq.c
> index 39599bbb5d45b6..f91dae16d69a19 100644
> --- a/drivers/net/ethernet/seeq/sgiseeq.c
> +++ b/drivers/net/ethernet/seeq/sgiseeq.c
> @@ -112,14 +112,18 @@ struct sgiseeq_private {
>  
>  static inline void dma_sync_desc_cpu(struct net_device *dev, void *addr)
>  {
> -	dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
> -		       DMA_FROM_DEVICE);
> +	struct sgiseeq_private *sp = netdev_priv(dev);
> +
> +	dma_sync_single_for_cpu(dev->dev.parent, VIRT_TO_DMA(sp, addr),
> +			sizeof(struct sgiseeq_rx_desc), DMA_BIDIRECTIONAL);
>  }
>  
>  static inline void dma_sync_desc_dev(struct net_device *dev, void *addr)
>  {
> -	dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
> -		       DMA_TO_DEVICE);
> +	struct sgiseeq_private *sp = netdev_priv(dev);
> +
> +	dma_sync_single_for_device(dev->dev.parent, VIRT_TO_DMA(sp, addr),
> +			sizeof(struct sgiseeq_rx_desc), DMA_BIDIRECTIONAL);
>  }

this breaks ethernet on IP22 completely, but I haven't figured out why, yet.

Thomas.
Thomas Bogendoerfer Sept. 1, 2020, 5:12 p.m. UTC | #2
On Tue, Sep 01, 2020 at 05:22:09PM +0200, Thomas Bogendoerfer wrote:
> On Wed, Aug 19, 2020 at 08:55:49AM +0200, Christoph Hellwig wrote:
> > Use the proper modern API to transfer cache ownership for incoherent DMA.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >  drivers/net/ethernet/seeq/sgiseeq.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/seeq/sgiseeq.c b/drivers/net/ethernet/seeq/sgiseeq.c
> > index 39599bbb5d45b6..f91dae16d69a19 100644
> > --- a/drivers/net/ethernet/seeq/sgiseeq.c
> > +++ b/drivers/net/ethernet/seeq/sgiseeq.c
> > @@ -112,14 +112,18 @@ struct sgiseeq_private {
> >  
> >  static inline void dma_sync_desc_cpu(struct net_device *dev, void *addr)
> >  {
> > -	dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
> > -		       DMA_FROM_DEVICE);
> > +	struct sgiseeq_private *sp = netdev_priv(dev);
> > +
> > +	dma_sync_single_for_cpu(dev->dev.parent, VIRT_TO_DMA(sp, addr),
> > +			sizeof(struct sgiseeq_rx_desc), DMA_BIDIRECTIONAL);
> >  }
> >  
> >  static inline void dma_sync_desc_dev(struct net_device *dev, void *addr)
> >  {
> > -	dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
> > -		       DMA_TO_DEVICE);
> > +	struct sgiseeq_private *sp = netdev_priv(dev);
> > +
> > +	dma_sync_single_for_device(dev->dev.parent, VIRT_TO_DMA(sp, addr),
> > +			sizeof(struct sgiseeq_rx_desc), DMA_BIDIRECTIONAL);
> >  }
> 
> this breaks ethernet on IP22 completely, but I haven't figured out why, yet.

the problem is that dma_sync_single_for_cpu() doesn't flush anything
for IP22, because it only flushes for CPUs which do speculation. So
either MIPS arch_sync_dma_for_cpu() should always flush or sgiseeq
needs to use a different sync funktion, when it wants to re-read descriptors
from memory.

Thomas.
Thomas Bogendoerfer Sept. 1, 2020, 5:38 p.m. UTC | #3
On Tue, Sep 01, 2020 at 07:16:27PM +0200, Christoph Hellwig wrote:
> Well, if IP22 doesn't speculate (which I'm pretty sure is the case),
> dma_sync_single_for_cpu should indeeed be a no-op.  But then there
> also shouldn't be anything in the cache, as the previous
> dma_sync_single_for_device should have invalidated it.  So it seems like
> we are missing one (or more) ownership transfers to the device.  I'll
> try to look at the the ownership management in a little more detail
> tomorrow.

this is the problem:

       /* Always check for received packets. */
        sgiseeq_rx(dev, sp, hregs, sregs);

so the driver will look at the rx descriptor on every interrupt, so
we cache the rx descriptor on the first interrupt and if there was
$no rx packet, we will only see it, if cache line gets flushed for
some other reason. kick_tx() does a busy loop checking tx descriptors,
with just sync_desc_cpu...

Thomas.
Christoph Hellwig Sept. 3, 2020, 8:42 a.m. UTC | #4
On Wed, Sep 02, 2020 at 11:38:09PM +0200, Thomas Bogendoerfer wrote:
> the patch below fixes the problem.

But is very wrong unfortunately.

>  static inline void dma_sync_desc_cpu(struct net_device *dev, void *addr)
>  {
> -       dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
> -                      DMA_FROM_DEVICE);
> +       struct sgiseeq_private *sp = netdev_priv(dev);
> +
> +       dma_sync_single_for_device(dev->dev.parent, VIRT_TO_DMA(sp, addr),
> +                       sizeof(struct sgiseeq_rx_desc), DMA_FROM_DEVICE);
>  }
>  
>  static inline void dma_sync_desc_dev(struct net_device *dev, void *addr)
>  {
> -       dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
> -                      DMA_TO_DEVICE);
> +       struct sgiseeq_private *sp = netdev_priv(dev);
> +
> +       dma_sync_single_for_device(dev->dev.parent, VIRT_TO_DMA(sp, addr),
> +                       sizeof(struct sgiseeq_rx_desc), DMA_TO_DEVICE);

This is not how the DMA API works.  You can only call
dma_sync_single_for_{device,cpu} with the direction that the memory
was mapped.  It then transfer ownership to the device or the cpu,
and the ownership of the memory is a fundamental concept that allows
for reasoning about the caching interaction.

>  }
>  
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]
---end quoted text---
Christoph Hellwig Sept. 3, 2020, 8:46 a.m. UTC | #5
On Thu, Sep 03, 2020 at 10:43:02AM +0200, Christoph Hellwig wrote:
> On Tue, Sep 01, 2020 at 07:38:10PM +0200, Thomas Bogendoerfer wrote:
> > this is the problem:
> > 
> >        /* Always check for received packets. */
> >         sgiseeq_rx(dev, sp, hregs, sregs);
> > 
> > so the driver will look at the rx descriptor on every interrupt, so
> > we cache the rx descriptor on the first interrupt and if there was
> > $no rx packet, we will only see it, if cache line gets flushed for
> > some other reason.
> 
> That means a transfer back to device ownership is missing after a
> (negative) check.

E.g. something like this for the particular problem, although there
might be other hiding elsewhere:

diff --git a/drivers/net/ethernet/seeq/sgiseeq.c b/drivers/net/ethernet/seeq/sgiseeq.c
index 8507ff2420143a..a1c7be8a0d1e5d 100644
--- a/drivers/net/ethernet/seeq/sgiseeq.c
+++ b/drivers/net/ethernet/seeq/sgiseeq.c
@@ -403,6 +403,8 @@ static inline void sgiseeq_rx(struct net_device *dev, struct sgiseeq_private *sp
 		rd = &sp->rx_desc[sp->rx_new];
 		dma_sync_desc_cpu(dev, rd);
 	}
+	dma_sync_desc_dev(dev, rd);
+
 	dma_sync_desc_cpu(dev, &sp->rx_desc[orig_end]);
 	sp->rx_desc[orig_end].rdma.cntinfo &= ~(HPCDMA_EOR);
 	dma_sync_desc_dev(dev, &sp->rx_desc[orig_end]);
diff mbox series

Patch

diff --git a/drivers/net/ethernet/seeq/sgiseeq.c b/drivers/net/ethernet/seeq/sgiseeq.c
index 39599bbb5d45b6..f91dae16d69a19 100644
--- a/drivers/net/ethernet/seeq/sgiseeq.c
+++ b/drivers/net/ethernet/seeq/sgiseeq.c
@@ -112,14 +112,18 @@  struct sgiseeq_private {
 
 static inline void dma_sync_desc_cpu(struct net_device *dev, void *addr)
 {
-	dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
-		       DMA_FROM_DEVICE);
+	struct sgiseeq_private *sp = netdev_priv(dev);
+
+	dma_sync_single_for_cpu(dev->dev.parent, VIRT_TO_DMA(sp, addr),
+			sizeof(struct sgiseeq_rx_desc), DMA_BIDIRECTIONAL);
 }
 
 static inline void dma_sync_desc_dev(struct net_device *dev, void *addr)
 {
-	dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
-		       DMA_TO_DEVICE);
+	struct sgiseeq_private *sp = netdev_priv(dev);
+
+	dma_sync_single_for_device(dev->dev.parent, VIRT_TO_DMA(sp, addr),
+			sizeof(struct sgiseeq_rx_desc), DMA_BIDIRECTIONAL);
 }
 
 static inline void hpc3_eth_reset(struct hpc3_ethregs *hregs)