From: Christoph Hellwig <hch@lst.de>
To: Matthew Wilcox <willy@infradead.org>
Cc: alsa-devel@alsa-project.org, linux-doc@vger.kernel.org,
nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
linux-mm@kvack.org, linux1394-devel@lists.sourceforge.net,
Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
linux-samsung-soc@vger.kernel.org,
Joonyoung Shim <jy0922.shim@samsung.com>,
linux-scsi@vger.kernel.org, Ben Skeggs <bskeggs@redhat.com>,
Matt Porter <mporter@kernel.crashing.org>,
linux-media@vger.kernel.org,
Mauro Carvalho Chehab <mchehab@kernel.org>,
linux-arm-kernel@lists.infradead.org,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
linux-parisc@vger.kernel.org, netdev@vger.kernel.org,
Seung-Woo Kim <sw0312.kim@samsung.com>,
linux-mips@vger.kernel.org, Tomasz Figa <tfiga@chromium.org>,
iommu@lists.linux-foundation.org,
Stefan Richter <stefanr@s5r6.in-berlin.de>
Subject: Re: a saner API for allocating DMA addressable pages v2
Date: Tue, 15 Sep 2020 08:36:18 +0200 [thread overview]
Message-ID: <20200915063618.GD19113@lst.de> (raw)
In-Reply-To: <20200914152617.GR6583@casper.infradead.org>
On Mon, Sep 14, 2020 at 04:26:17PM +0100, Matthew Wilcox wrote:
> On Mon, Sep 14, 2020 at 04:44:16PM +0200, Christoph Hellwig wrote:
> > I'm still a little unsure about the API naming, as alloc_pages sort of
> > implies a struct page return value, but we return a kernel virtual
> > address.
>
> Erm ... dma_alloc_pages() returns a struct page, so is this sentence
> stale?
Yes.
> You say that like it's a bad thing. I think the problem is more that
> people don't understand what non-coherent means and think they're
> supporting it when they're not.
>
> dma_alloc_manual_flushing()?
That sounds pretty awkward..
>
> > As a follow up I plan to move the implementation of the
> > DMA_ATTR_NO_KERNEL_MAPPING flag over to this framework as well, given
> > that is also is a fundamentally non coherent allocation. The replacement
> > for that flag would then return a struct page, as it is allowed to
> > actually return pages without a kernel mapping as the name suggested
> > (although most of the time they will actually have a kernel mapping..)
>
> If the page doesn't have a kernel mapping, shouldn't it return a PFN
> or a phys_addr?
Most APIs we'll feed it into need a struct page. The difference is just
that it can be a highmem page. And if we want to get fancy we could
change the kernel mapping to PROT_NONE eventually.
prev parent reply other threads:[~2020-09-15 6:37 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-14 14:44 a saner API for allocating DMA addressable pages v2 Christoph Hellwig
2020-09-14 14:44 ` [PATCH 01/17] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT flag Christoph Hellwig
2020-09-14 14:44 ` [PATCH 02/17] mm: turn alloc_pages into an inline function Christoph Hellwig
2020-09-14 14:44 ` [PATCH 03/17] drm/exynos: stop setting DMA_ATTR_NON_CONSISTENT Christoph Hellwig
[not found] ` <7a1d11c2-0fc5-e110-dabe-960e516bb343@gmail.com>
2020-09-15 6:33 ` Christoph Hellwig
2020-09-14 14:44 ` [PATCH 04/17] drm/nouveau/gk20a: " Christoph Hellwig
2020-09-14 14:44 ` [PATCH 05/17] net/au1000-eth: stop using DMA_ATTR_NON_CONSISTENT Christoph Hellwig
2020-09-14 14:44 ` [PATCH 06/17] lib82596: move DMA allocation into the callers of i82596_probe Christoph Hellwig
2020-09-14 14:44 ` [PATCH 07/17] 53c700: improve non-coherent DMA handling Christoph Hellwig
2020-09-14 15:20 ` James Bottomley
2020-09-15 6:27 ` Christoph Hellwig
2020-09-15 14:10 ` James Bottomley
2020-09-14 14:44 ` [PATCH 08/17] dma-mapping: add a new dma_alloc_noncoherent API Christoph Hellwig
2020-09-14 14:44 ` [PATCH 09/17] sgiwd93: convert to dma_alloc_noncoherent Christoph Hellwig
2020-09-14 14:44 ` [PATCH 10/17] hal2: " Christoph Hellwig
2020-09-14 14:44 ` [PATCH 11/17] sgiseeq: " Christoph Hellwig
2020-09-14 15:13 ` Matthew Wilcox
2020-09-15 6:32 ` Christoph Hellwig
2020-09-14 14:44 ` [PATCH 12/17] 53c700: " Christoph Hellwig
2020-09-14 14:44 ` [PATCH 13/17] dma-mapping: remove dma_cache_sync Christoph Hellwig
2020-09-14 14:44 ` [PATCH 14/17] dma-mapping: add a new dma_alloc_pages API Christoph Hellwig
2020-09-14 14:44 ` [PATCH 15/17] dma-mapping: add new {alloc, free}_noncoherent dma_map_ops methods Christoph Hellwig
2020-09-14 14:44 ` [PATCH 16/17] dma-iommu: implement ->alloc_noncoherent Christoph Hellwig
2020-09-14 14:44 ` [PATCH 17/17] firewire-ohci: use dma_alloc_pages Christoph Hellwig
2020-09-14 15:26 ` a saner API for allocating DMA addressable pages v2 Matthew Wilcox
2020-09-15 6:36 ` Christoph Hellwig [this message]
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