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From: Christoph Hellwig <hch@lst.de>
To: Tomasz Figa <tfiga@chromium.org>
Cc: Christoph Hellwig <hch@lst.de>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
	Joonyoung Shim <jy0922.shim@samsung.com>,
	Seung-Woo Kim <sw0312.kim@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Ben Skeggs <bskeggs@redhat.com>, Pawel Osciak <pawel@osciak.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Matt Porter <mporter@kernel.crashing.org>,
	"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,"
	<iommu@lists.linux-foundation.org>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	alsa-devel@alsa-project.org,
	linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
	linux-ia64@vger.kernel.org, linux-scsi@vger.kernel.org,
	linux-parisc@vger.kernel.org,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	nouveau@lists.freedesktop.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-nvme@lists.infradead.org, linux-mips@vger.kernel.org,
	linux-mm@kvack.org, netdev@vger.kernel.org,
	"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,"
	<linux-arm-kernel@lists.infradead.org>,
	Linux Media Mailing List <linux-media@vger.kernel.org>
Subject: Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT
Date: Thu, 20 Aug 2020 06:43:47 +0200	[thread overview]
Message-ID: <20200820044347.GA4533@lst.de> (raw)
In-Reply-To: <CAAFQd5BuXP7t3d-Rwft85j=KTyXq7y4s24mQxLr=VoY9krEGZw@mail.gmail.com>

On Wed, Aug 19, 2020 at 03:57:53PM +0200, Tomasz Figa wrote:
> > > Could you explain what makes you think it's unused? It's a feature of
> > > the UAPI generally supported by the videobuf2 framework and relied on
> > > by Chromium OS to get any kind of reasonable performance when
> > > accessing V4L2 buffers in the userspace.
> >
> > Because it doesn't do anything except on PARISC and non-coherent MIPS,
> > so by definition it isn't used by any of these media drivers.
> 
> It's still an UAPI feature, so we can't simply remove the flag, it
> must stay there as a no-op, until the problem is resolved.

Ok, I'll switch to just ignoring it for the next version.

> Also, it of course might be disputable as an out-of-tree usage, but
> selecting CONFIG_DMA_NONCOHERENT_CACHE_SYNC makes the flag actually do
> something on other platforms, including ARM64.

It isn't just disputable, but by kernel policies simply is not relevant.

  reply	other threads:[~2020-08-20  4:43 UTC|newest]

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200819065610eucas1p2fde88e81917071b1888e7cc01ba0f298@eucas1p2.samsung.com>
2020-08-19  6:55 ` a saner API for allocating DMA addressable pages Christoph Hellwig
2020-08-19  6:55   ` [PATCH 01/28] mm: turn alloc_pages into an inline function Christoph Hellwig
2020-08-19  6:55   ` [PATCH 02/28] drm/exynos: stop setting DMA_ATTR_NON_CONSISTENT Christoph Hellwig
2020-08-19  6:55   ` [PATCH 03/28] drm/nouveau/gk20a: " Christoph Hellwig
2020-08-19  6:55   ` [PATCH 04/28] net/au1000-eth: stop using DMA_ATTR_NON_CONSISTENT Christoph Hellwig
2020-08-19  6:55   ` [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT Christoph Hellwig
2020-08-19 11:16     ` Tomasz Figa
2020-08-19 11:51       ` Robin Murphy
2020-08-19 12:49         ` Tomasz Figa
2020-08-19 13:57           ` Christoph Hellwig
2020-08-19 14:11             ` Tomasz Figa
2020-08-20  4:45               ` Christoph Hellwig
2020-08-20 10:09                 ` Tomasz Figa
2020-08-20 16:51                   ` Christoph Hellwig
2020-08-19 14:07           ` Robin Murphy
2020-08-19 14:22             ` Tomasz Figa
2020-08-20  4:52               ` Christoph Hellwig
2020-08-20  5:02             ` Christoph Hellwig
2020-08-20 10:24               ` Tomasz Figa
2020-08-20 16:52                 ` Christoph Hellwig
2020-08-20 17:41                   ` Tomasz Figa
2020-08-19 13:54       ` Christoph Hellwig
2020-08-19 13:57         ` Tomasz Figa
2020-08-20  4:43           ` Christoph Hellwig [this message]
2020-08-20  5:20             ` Christoph Hellwig
2020-08-20 10:05               ` Tomasz Figa
2020-08-20 16:54                 ` Christoph Hellwig
2020-08-20 17:33                   ` Tomasz Figa
2020-09-01 11:06                     ` Christoph Hellwig
2020-09-01 15:02                       ` Tomasz Figa
2020-08-19  6:55   ` [PATCH 06/28] lib82596: move DMA allocation into the callers of i82596_probe Christoph Hellwig
2020-09-01 13:29     ` Thomas Bogendoerfer
2020-08-19  6:55   ` [PATCH 07/28] 53c700: improve non-coherent DMA handling Christoph Hellwig
2020-09-01 14:52     ` James Bottomley
2020-09-01 15:05       ` Matthew Wilcox
2020-09-01 15:22         ` James Bottomley
2020-09-01 16:21           ` Helge Deller
2020-09-01 16:41             ` Helge Deller
2020-09-01 16:53               ` Matthew Wilcox
2020-09-02 15:00                 ` Helge Deller
2020-08-19  6:55   ` [PATCH 08/28] MIPS: make dma_sync_*_for_cpu a little less overzealous Christoph Hellwig
2020-09-01 13:53     ` Thomas Bogendoerfer
2020-08-19  6:55   ` [PATCH 09/28] MIPS/jazzdma: remove the unused vdma_remap function Christoph Hellwig
2020-09-01 13:49     ` Thomas Bogendoerfer
2020-08-19  6:55   ` [PATCH 10/28] MIPS/jazzdma: decouple from dma-direct Christoph Hellwig
2020-09-01 13:49     ` Thomas Bogendoerfer
2020-08-19  6:55   ` [PATCH 11/28] dma-mapping: add (back) arch_dma_mark_clean for ia64 Christoph Hellwig
2020-08-19  6:55   ` [PATCH 12/28] dma-direct: remove dma_direct_{alloc,free}_pages Christoph Hellwig
2020-08-19  6:55   ` [PATCH 13/28] dma-direct: lift gfp_t manipulation out of__dma_direct_alloc_pages Christoph Hellwig
2020-08-19  6:55   ` [PATCH 14/28] dma-direct: use phys_to_dma_direct in dma_direct_alloc Christoph Hellwig
2020-08-19  6:55   ` [PATCH 15/28] dma-direct: remove __dma_to_phys Christoph Hellwig
2020-08-19  6:55   ` [PATCH 16/28] dma-direct: rename and cleanup __phys_to_dma Christoph Hellwig
2020-08-19  6:55   ` [PATCH 17/28] dma-mapping: move dma_common_{mmap,get_sgtable} out of mapping.c Christoph Hellwig
2020-08-19  6:55   ` [PATCH 18/28] dma-mapping: move the dma_declare_coherent_memory documentation Christoph Hellwig
2020-08-19  6:55   ` [PATCH 19/28] dma-mapping: replace DMA_ATTR_NON_CONSISTENT with dma_{alloc,free}_pages Christoph Hellwig
2020-08-19 15:03     ` [PATCH 19/28] dma-mapping: replace DMA_ATTR_NON_CONSISTENT with dma_{alloc, free}_pages Tomasz Figa
2020-08-20  5:15       ` Christoph Hellwig
2020-08-19  6:55   ` [PATCH 20/28] sgiwd93: convert from dma_cache_sync to dma_sync_single_for_device Christoph Hellwig
2020-08-19  6:55   ` [PATCH 21/28] hal2: " Christoph Hellwig
2020-08-19  6:55   ` [PATCH 22/28] sgiseeq: " Christoph Hellwig
2020-09-01 15:22     ` Thomas Bogendoerfer
2020-09-01 17:12       ` Thomas Bogendoerfer
2020-09-01 17:16         ` Christoph Hellwig
2020-09-01 17:38           ` Thomas Bogendoerfer
2020-09-02 21:38             ` Thomas Bogendoerfer
2020-09-03  8:42               ` Christoph Hellwig
2020-09-03  8:43             ` Christoph Hellwig
2020-09-03  8:46               ` Christoph Hellwig
2020-08-19  6:55   ` [PATCH 23/28] lib82596: " Christoph Hellwig
2020-08-19  6:55   ` [PATCH 24/28] 53c700: " Christoph Hellwig
2020-08-19  6:55   ` [PATCH 25/28] dma-mapping: remove dma_cache_sync Christoph Hellwig
2020-08-19  6:55   ` [PATCH 26/28] dmapool: add dma_alloc_pages support Christoph Hellwig
2020-08-19  6:55   ` [PATCH 27/28] nvme-pci: fix PRP pool size Christoph Hellwig
2020-08-19  6:55   ` [PATCH 28/28] nvme-pci: use dma_alloc_pages backed dmapools Christoph Hellwig
2020-08-25 11:30   ` a saner API for allocating DMA addressable pages Marek Szyprowski
2020-08-25 13:26     ` Christoph Hellwig
2020-08-29  9:46   ` Helge Deller

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