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From: Christoph Hellwig <hch@lst.de>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: sumit.garg@linaro.org, daniel.thompson@linaro.org,
	obayashi.yoshimasa@socionext.com, stable@vger.kernel.org,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	robin.murphy@arm.com, hch@lst.de
Subject: Re: DMA direct mapping fix for 5.4 and earlier stable branches
Date: Tue, 9 Feb 2021 10:36:42 +0100	[thread overview]
Message-ID: <20210209093642.GA1006@lst.de> (raw)
In-Reply-To: <YCJUgKDNVjJ4dUqM@kroah.com>

On Tue, Feb 09, 2021 at 10:23:12AM +0100, Greg KH wrote:
> >   From the view point of ZeroCopy using DMABUF, is 5.4 not 
> > mature enough, and is 5.10 enough mature ?
> >   This is the most important point for judging migration.
> 
> How do you judge "mature"?
> 
> And again, if a feature isn't present in a specific kernel version, why
> would you think that it would be a viable solution for you to use?

I'm pretty sure dma_get_sgtable has been around much longer and was
supposed to work, but only really did work properly for arm32, and
for platforms with coherent DMA.  I bet he is using non-coherent arm64,
and it would be broken for other drivers there as well if people did
test them, which they apparently so far did not.
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WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: obayashi.yoshimasa@socionext.com, sumit.garg@linaro.org,
	hch@lst.de, m.szyprowski@samsung.com, robin.murphy@arm.com,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org, daniel.thompson@linaro.org
Subject: Re: DMA direct mapping fix for 5.4 and earlier stable branches
Date: Tue, 9 Feb 2021 10:36:42 +0100	[thread overview]
Message-ID: <20210209093642.GA1006@lst.de> (raw)
In-Reply-To: <YCJUgKDNVjJ4dUqM@kroah.com>

On Tue, Feb 09, 2021 at 10:23:12AM +0100, Greg KH wrote:
> >   From the view point of ZeroCopy using DMABUF, is 5.4 not 
> > mature enough, and is 5.10 enough mature ?
> >   This is the most important point for judging migration.
> 
> How do you judge "mature"?
> 
> And again, if a feature isn't present in a specific kernel version, why
> would you think that it would be a viable solution for you to use?

I'm pretty sure dma_get_sgtable has been around much longer and was
supposed to work, but only really did work properly for arm32, and
for platforms with coherent DMA.  I bet he is using non-coherent arm64,
and it would be broken for other drivers there as well if people did
test them, which they apparently so far did not.

  reply	other threads:[~2021-02-09  9:36 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09  6:09 DMA direct mapping fix for 5.4 and earlier stable branches Sumit Garg
2021-02-09  6:09 ` Sumit Garg
2021-02-09  6:58 ` Greg Kroah-Hartman
2021-02-09  6:58   ` Greg Kroah-Hartman
2021-02-09  7:58   ` Sumit Garg
2021-02-09  8:04     ` Greg Kroah-Hartman
2021-02-09  8:04       ` Greg Kroah-Hartman
2021-02-09  9:05       ` obayashi.yoshimasa
2021-02-09  9:23         ` Greg KH
2021-02-09  9:23           ` Greg KH
2021-02-09  9:36           ` Christoph Hellwig [this message]
2021-02-09  9:36             ` Christoph Hellwig
2021-02-09 12:36             ` Sumit Garg
2021-02-09 12:36               ` Sumit Garg
2021-02-09 12:45               ` Robin Murphy
2021-02-09 12:45                 ` Robin Murphy
2021-02-09 15:50                 ` Christoph Hellwig
2021-02-09 15:50                   ` Christoph Hellwig
2021-02-09 10:19           ` obayashi.yoshimasa
2021-02-09 10:19             ` obayashi.yoshimasa
2021-02-09 10:39             ` Greg KH
2021-02-09 10:39               ` Greg KH

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