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

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Date:	Fri, 06 Jun 2014 19:21:38 +0300
From:	Eli Billauer <eli.billauer@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Joerg Roedel <joro@...tes.org>, devel@...verdev.osuosl.org,
	Shuah Khan <shuah.kh@...sung.com>, discuss@...-64.org,
	linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
	iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v2 1/4] dma-mapping: Add devm_ interface for
 dma_map_single()

On 06/06/14 19:01, Greg KH wrote:
>> Please try to put yourself in my position: I have a driver that I care
>> >  about, which works fine for a few years. It's based upon dma_map_single(),
>> >  which seems to be the common way to get non-coherent memory, even for the
>> >  driver's entire lifespan. I realize that dma_alloc_* was the intended way to
>> >  do it, but fact is that dma_map_* has become the common choice.
>>
> Is your driver in the kernel tree?  If not, you really are on your own :(
>
It's the Xillybus driver in the staging area. I don't know if this 
counts for being in the kernel tree...

The suggested patchset would allow replacing my use of dma_map_single() 
with a managed version of that function. This will clean the driver's 
code considerably.

But I think that the discussion here is if it's valid to use 
dma_map_single() for a device-permanent DMA mapping, or if 
dma_alloc_noncoherent() is the only way. If the answer is no, there's 
quite obviously no point in a devres version for that function.

Regards,
    Eli
> greg k-h
>
>


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