linux-kernel - Re: [PATCH v2 1/4] dma-mapping: Add devm_ interface for dma_map

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Message-ID: <20140604141211.GC23880@8bytes.org>
Date:	Wed, 4 Jun 2014 16:12:11 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Shuah Khan <shuah.kh@...sung.com>,
	Eli Billauer <eli.billauer@...il.com>,
	devel@...verdev.osuosl.org, gregkh@...uxfoundation.org,
	bhelgaas@...gle.com, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
	discuss@...-64.org
Subject: Re: [PATCH v2 1/4] dma-mapping: Add devm_ interface for
 dma_map_single()

On Wed, Jun 04, 2014 at 10:04:08AM -0400, Tejun Heo wrote:
> Hmmm?  Don't we have drivers which map dma buffers on device init and
> release them on exit?  For dynamic usages, its usefulness is limited
> especially given that dynamic tracking of buffers usually would
> involve tracking of other information too in addition to dma buffer
> pointer themselves.  If alloc on init and free on exit is a very rare
> usage pattern, I have no objection against not adding devm interface
> for dma mappings.

Yes, but those drivers usually get DMA buffers at init time with the
dma_alloc_* interfaces. The dma_map_* interfaces discussed here belong
to the streaming DMA-API, so they are usually used for only one DMA
transaction before dma_unmap_* is called on them.

A devm interface for the dma_alloc_* family of functions would
actually make sense, but not for the dma_map_* functions.


	Joerg


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