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Message-id: <5391EA92.9050306@gmail.com>
Date: Fri, 06 Jun 2014 19:21:38 +0300
From: Eli Billauer <eli.billauer@gmail.com>
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To: Greg KH <gregkh@linuxfoundation.org>
Cc: Joerg Roedel <joro@8bytes.org>, devel@driverdev.osuosl.org,
        Shuah Khan <shuah.kh@samsung.com>, discuss@x86-64.org,
        linux-kernel@vger.kernel.org, bhelgaas@google.com,
        iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org,
        Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v2 1/4] dma-mapping: Add devm_ interface for
 dma_map_single()
References: <1401606077-1739-1-git-send-email-eli.billauer@gmail.com>
 <1401606077-1739-2-git-send-email-eli.billauer@gmail.com>
 <538E3D04.9060808@samsung.com> <20140603233907.GB23880@8bytes.org>
 <20140604140408.GC5004@htj.dyndns.org> <20140604141211.GC23880@8bytes.org>
 <20140604141416.GD5004@htj.dyndns.org> <538F3548.4050101@gmail.com>
 <20140604212525.GE23880@8bytes.org> <5391A9C2.3040602@gmail.com>
 <20140606160103.GG15110@kroah.com>
In-reply-to: <20140606160103.GG15110@kroah.com>
Sender: linux-kernel-owner@vger.kernel.org

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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