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Date: Tue, 1 Sep 2020 19:38:10 +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 07:16:27PM +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. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]
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