linux-kernel - Re: [PATCH 22/28] sgiseeq: convert from dma_cache_sync to dma_sync_single_for

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Message-ID: <20200901171241.GA20685@alpha.franken.de>
Date:   Tue, 1 Sep 2020 19:12:41 +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 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@....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.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]