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Date:   Wed, 2 Sep 2020 23:38:09 +0200
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Christoph Hellwig <hch@....de>
Cc:     alsa-devel@...a-project.org, linux-ia64@...r.kernel.org,
        linux-doc@...r.kernel.org, nouveau@...ts.freedesktop.org,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        linux-mm@...ck.org, Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-samsung-soc@...r.kernel.org,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        linux-scsi@...r.kernel.org,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Matt Porter <mporter@...nel.crashing.org>,
        linux-media@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Pawel Osciak <pawel@...iak.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-parisc@...r.kernel.org,
        netdev@...r.kernel.org, Seung-Woo Kim <sw0312.kim@...sung.com>,
        linux-mips@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 22/28] sgiseeq: convert from dma_cache_sync to
 dma_sync_single_for_device

On Tue, Sep 01, 2020 at 07:38:10PM +0200, Thomas Bogendoerfer wrote:
> 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...

the patch below fixes the problem.

Thomas.


diff --git a/drivers/net/ethernet/seeq/sgiseeq.c b/drivers/net/ethernet/seeq/sgiseeq.c
index 8507ff242014..876e3700a0e4 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_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);
 }
 
-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]

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