From: Tomasz Figa <tfiga@chromium.org>
To: Christoph Hellwig <hch@lst.de>
Cc: linux-media@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 8/8] WIP: add a dma_alloc_contiguous API
Date: Fri, 2 Oct 2020 17:50:40 +0000 [thread overview]
Message-ID: <20201002175040.GA1131147@chromium.org> (raw)
In-Reply-To: <20200930160917.1234225-9-hch@lst.de>
Hi Christoph,
On Wed, Sep 30, 2020 at 06:09:17PM +0200, Christoph Hellwig wrote:
> Add a new API that returns a virtually non-contigous array of pages
> and dma address. This API is only implemented for dma-iommu and will
> not be implemented for non-iommu DMA API instances that have to allocate
> contiguous memory. It is up to the caller to check if the API is
> available.
Would you mind scheding some more light on what made the previous attempt
not work well? I liked the previous API because it was more consistent with
the regular dma_alloc_coherent().
>
> The intent is that media drivers can use this API if either:
FWIW, the USB subsystem also has similar needs, and so do some DRM drivers
using DMA API rather than IOMMU API directly. Basically I believe that all
the users removed in your previous series relied on custom downstream
patches to make DMA_ATTR_NON_CONSISTENT work and could be finally made work
in upstream using this API.
>
> - no kernel mapping or only temporary kernel mappings are required.
> That is as a better replacement for DMA_ATTR_NO_KERNEL_MAPPING
> - a kernel mapping is required for cached and DMA mapped pages, but
> the driver also needs the pages to e.g. map them to userspace.
> In that sense it is a replacement for some aspects of the recently
> removed and never fully implemented DMA_ATTR_NON_CONSISTENT
What's the expected allocation and mapping flow with the latter? Would that be
pages = dma_alloc_noncoherent(...)
vaddr = vmap(pages, ...);
?
Would one just use the usual dma_sync_for_{cpu,device}() for cache
invallidate/clean, while keeping the mapping in place?
Best regards,
Tomasz
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next prev parent reply other threads:[~2020-10-02 17:50 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-30 16:09 dma_alloc_pages / dma_alloc_noncoherent fixups Christoph Hellwig
2020-09-30 16:09 ` [PATCH 1/8] dma-mapping: remove the {alloc,free}_noncoherent methods Christoph Hellwig
2020-09-30 16:09 ` [PATCH 2/8] dma-mapping: document dma_{alloc,free}_pages Christoph Hellwig
2020-09-30 16:09 ` [PATCH 3/8] dma-direct check for highmem pages in dma_direct_alloc_pages Christoph Hellwig
2020-09-30 16:09 ` [PATCH 4/8] dma-direct: use __GFP_ZERO " Christoph Hellwig
2020-10-06 7:24 ` Hillf Danton
2020-09-30 16:09 ` [PATCH 5/8] dma-direct: factor out a dma_direct_alloc_from_pool helper Christoph Hellwig
2020-09-30 16:09 ` [PATCH 6/8] dma-direct: simplify the DMA_ATTR_NO_KERNEL_MAPPING handling Christoph Hellwig
2020-09-30 16:09 ` [PATCH 7/8] dma-iommu: remove __iommu_dma_mmap Christoph Hellwig
2020-09-30 16:09 ` [PATCH 8/8] WIP: add a dma_alloc_contiguous API Christoph Hellwig
2020-10-02 17:50 ` Tomasz Figa [this message]
2020-10-05 8:26 ` Christoph Hellwig
2020-10-06 20:56 ` Tomasz Figa
2020-10-07 6:21 ` Christoph Hellwig
2020-10-07 12:21 ` Tomasz Figa
2020-10-07 12:24 ` Christoph Hellwig
2020-10-14 13:20 ` Tomasz Figa
2020-10-14 15:03 ` David Laight
2020-11-09 14:53 ` Ricardo Ribalda
2020-11-10 9:25 ` Christoph Hellwig
2020-11-10 9:33 ` Ricardo Ribalda
2020-11-10 9:41 ` Christoph Hellwig
2020-11-10 9:50 ` Tomasz Figa
2020-11-10 9:57 ` Christoph Hellwig
2020-11-17 21:21 ` Ricardo Ribalda
2020-11-18 14:25 ` [PATCH] WIP! media: uvcvideo: Use dma_alloc_noncontiguos API Ricardo Ribalda
2020-11-24 11:35 ` Christoph Hellwig
2020-11-24 12:01 ` Ricardo Ribalda
2020-11-24 13:33 ` Christoph Hellwig
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