From: David Laight <David.Laight@ACULAB.COM>
To: 'Robin Murphy' <robin.murphy@arm.com>, 'Christoph Hellwig' <hch@lst.de>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>,
Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
David Airlie <airlied@linux.ie>,
"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
Intel Linux Wireless <linuxwifi@intel.com>,
"intel-gfx@lists.freedesktop.org"
<intel-gfx@lists.freedesktop.org>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Jani Nikula <jani.nikula@linux.intel.com>,
Ian Abbott <abbotti@mev.co.uk>,
Rodrigo Vivi <rodrigo.vivi@intel.com>,
Sean Paul <sean@poorly.run>,
"moderated list:ARM PORT" <linux-arm-kernel@lists.infradead.org>,
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"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
H Hartley Sweeten <hsweeten@visionengravers.com>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
Daniel Vetter <daniel@ffwll.ch>
Subject: RE: [PATCH 16/16] dma-mapping: use exact allocation in dma_alloc_contiguous
Date: Fri, 14 Jun 2019 15:16:43 +0000 [thread overview]
Message-ID: <d8009432a10549bbbda802021562a28b@AcuMS.aculab.com> (raw)
In-Reply-To: <4113cd5f-5c13-e9c7-bc5e-dcf0b60e7054@arm.com>
From: Robin Murphy
> Sent: 14 June 2019 16:06
...
> Well, apart from the bit in DMA-API-HOWTO which has said this since
> forever (well, before Git history, at least):
>
> "The CPU virtual address and the DMA address are both
> guaranteed to be aligned to the smallest PAGE_SIZE order which
> is greater than or equal to the requested size. This invariant
> exists (for example) to guarantee that if you allocate a chunk
> which is smaller than or equal to 64 kilobytes, the extent of the
> buffer you receive will not cross a 64K boundary."
I knew it was somewhere :-)
Interestingly that also implies that the address returned for a size
of (say) 128 will also be page aligned.
In that case 128 byte alignment should probably be ok - but it is still
an API change that could have horrid consequences.
David
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Registration No: 1397386 (Wales)
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next prev parent reply other threads:[~2019-06-14 15:16 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-14 13:47 use exact allocation for dma coherent memory Christoph Hellwig
2019-06-14 13:47 ` [PATCH 01/16] media: videobuf-dma-contig: use dma_mmap_coherent Christoph Hellwig
2019-06-14 13:47 ` [PATCH 02/16] drm/ati_pcigart: stop using drm_pci_alloc Christoph Hellwig
2019-06-14 13:47 ` [PATCH 03/16] drm/i915: " Christoph Hellwig
2019-06-14 16:45 ` [Intel-gfx] " Ville Syrjälä
2019-06-14 13:47 ` [PATCH 04/16] drm: move drm_pci_{alloc,free} to drm_legacy Christoph Hellwig
2019-06-14 13:47 ` [PATCH 05/16] drm: don't mark pages returned from drm_pci_alloc reserved Christoph Hellwig
2019-06-14 13:47 ` [PATCH 06/16] drm: don't pass __GFP_COMP to dma_alloc_coherent in drm_pci_alloc Christoph Hellwig
2019-06-14 13:47 ` [PATCH 07/16] IB/hfi1: stop passing bogus gfp flags arguments to dma_alloc_coherent Christoph Hellwig
2019-06-14 13:47 ` [PATCH 08/16] IB/qib: " Christoph Hellwig
2019-06-14 13:47 ` [PATCH 09/16] cnic: " Christoph Hellwig
2019-06-14 13:47 ` [PATCH 10/16] iwlwifi: " Christoph Hellwig
2019-06-14 13:47 ` [PATCH 11/16] s390/ism: " Christoph Hellwig
2019-06-14 13:47 ` [PATCH 12/16] staging/comedi: mark as broken Christoph Hellwig
2019-06-14 14:02 ` Greg KH
2019-06-14 14:48 ` Christoph Hellwig
2019-06-14 15:30 ` Greg KH
2019-06-14 15:34 ` Christoph Hellwig
2019-06-17 13:15 ` Ian Abbott
2019-06-14 13:47 ` [PATCH 13/16] mm: rename alloc_pages_exact_nid to alloc_pages_exact_node Christoph Hellwig
2019-06-14 13:47 ` [PATCH 14/16] mm: use alloc_pages_exact_node to implement alloc_pages_exact Christoph Hellwig
2019-06-14 13:47 ` [PATCH 15/16] dma-mapping: clear __GFP_COMP in dma_alloc_attrs Christoph Hellwig
2019-06-14 13:47 ` [PATCH 16/16] dma-mapping: use exact allocation in dma_alloc_contiguous Christoph Hellwig
2019-06-14 14:15 ` David Laight
2019-06-14 14:50 ` 'Christoph Hellwig'
2019-06-14 15:01 ` David Laight
2019-06-14 15:05 ` 'Christoph Hellwig'
2019-06-14 15:05 ` Robin Murphy
2019-06-14 15:08 ` 'Christoph Hellwig'
2019-06-14 15:16 ` David Laight [this message]
2019-06-17 8:21 ` use exact allocation for dma coherent memory Dan Carpenter
2019-06-17 8:33 ` Christoph Hellwig
2019-06-19 16:29 ` Jason Gunthorpe
2019-06-20 10:51 ` Christoph Hellwig
2019-07-01 8:48 ` Christoph Hellwig
2019-07-02 9:48 ` Arend Van Spriel
2019-07-08 18:43 ` Christoph Hellwig
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