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Date: Mon, 2 Oct 2023 10:46:05 +0200
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Jerry Snitselaar <jsnitsel@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Hannes Reinecke <hare@suse.de>,
	Chris Leech <cleech@redhat.com>, Rasesh Mody <rmody@marvell.com>,
	Ariel Elior <aelior@marvell.com>,
	Sudarsana Kalluru <skalluru@marvell.com>,
	Manish Chopra <manishc@marvell.com>,
	Nilesh Javali <njavali@marvell.com>,
	Manish Rangankar <mrangankar@marvell.com>,
	John Meneghini <jmeneghi@redhat.com>, Lee Duncan <lduncan@suse.com>,
	Mike Christie <michael.christie@oracle.com>,
	Hannes Reinecke <hare@kernel.org>, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] cnic,bnx2,bnx2x: use UIO_MEM_DMA_COHERENT
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In-Reply-To: <tf2zu6gqaii2bjipbo2mn2hz64px2624rfcmyg36rkq4bskxiw@zgjzznig6e22>

On Mon, Oct 02, 2023 at 12:50:21AM -0700, Jerry Snitselaar wrote:
> On Mon, Oct 02, 2023 at 08:04:24AM +0200, Christoph Hellwig wrote:
> > On Sun, Oct 01, 2023 at 07:22:36AM -0700, Jerry Snitselaar wrote:
> > > Changes last year to the dma-mapping api to no longer allow __GFP_COMP,
> > > in particular these two (from the e529d3507a93 dma-mapping pull for
> > > 6.2):
> > 
> > That's complete BS.  The driver was broken since day 1 and always
> > ignored the DMA API requirement to never try to grab the page from the
> > dma coherent allocation because you generally speaking can't.  It just
> > happened to accidentally work the trivial dma coherent allocator that
> > is used on x86.
> > 
> 
> re-sending since gmail decided to not send plain text:
> 
> Yes, I agree that it has been broken and misusing the API. Greg's
> question was what changed though, and it was the clean up of
> __GFP_COMP in dma-mapping that brought the problem in the driver to
> light.
> 
> I already said the other day that cnic has been doing this for 14
> years. I'm not blaming you or your __GFP_COMP cleanup commits, they
> just uncovered that cnic was doing something wrong. My apologies if
> you took it that way.

As these devices aren't being made anymore, and this api is really not a
good idea in the first place, why don't we just leave it broken and see
if anyone notices?

thanks,

greg k-h