linux-kernel - Re: [PATCH 3/3] cnic,bnx2,bnx2x: use UIO_MEM_DMA

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Date:   Mon, 2 Oct 2023 10:59:15 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jerry Snitselaar <jsnitsel@...hat.com>
Cc:     Christoph Hellwig <hch@....de>, Chris Leech <cleech@...hat.com>,
        Rasesh Mody <rmody@...vell.com>,
        Ariel Elior <aelior@...vell.com>,
        Sudarsana Kalluru <skalluru@...vell.com>,
        Manish Chopra <manishc@...vell.com>,
        Nilesh Javali <njavali@...vell.com>,
        Manish Rangankar <mrangankar@...vell.com>,
        John Meneghini <jmeneghi@...hat.com>,
        Lee Duncan <lduncan@...e.com>,
        Mike Christie <michael.christie@...cle.com>,
        Hannes Reinecke <hare@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] cnic,bnx2,bnx2x: use UIO_MEM_DMA_COHERENT

On 10/2/23 10:46, Greg Kroah-Hartman wrote:
> 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?
> 
Guess what triggered this mail thread.
Some customers did notice.

Problem is that these devices were built as the network interface in 
some bladecenter machines, so you can't just replace them with a 
different Ethernet card.

Cheers,

Hannes