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From: Andy Shevchenko <andy.shevchenko@gmail.com>
Date: Fri, 3 Aug 2018 21:38:41 +0300
Message-ID: <CAHp75VfZfhHS1Hgrm+3xJL=3gT9Bri16JJSFUJpDY0=Ev5X-PA@mail.gmail.com>
Subject: Re: [PATCH v2 2/9] dmapool: cleanup error messages
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Sender: owner-linux-mm@kvack.org
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To: Tony Battersby <tonyb@cybernetics.com>
Cc: Matthew Wilcox <willy@infradead.org>, Christoph Hellwig <hch@lst.de>, Marek Szyprowski <m.szyprowski@samsung.com>, Sathya Prakash <sathya.prakash@broadcom.com>, Chaitra P B <chaitra.basappa@broadcom.com>, Suganath Prabu Subramani <suganath-prabu.subramani@broadcom.com>, iommu@lists.linux-foundation.org, linux-mm <linux-mm@kvack.org>, linux-scsi <linux-scsi@vger.kernel.org>, MPT-FusionLinux.pdl@broadcom.com

On Fri, Aug 3, 2018 at 8:03 PM, Tony Battersby <tonyb@cybernetics.com> wrote:
> On 08/03/2018 12:22 PM, Matthew Wilcox wrote:
>> On Fri, Aug 03, 2018 at 06:59:20PM +0300, Andy Shevchenko wrote:
>>>>>> I'm pretty sure this was created in an order to avoid bad looking (and
>>>>>> in some cases frightening) "NULL device *" part.
>>> JFYI: git log --no-merges --grep 'NULL device \*'
>> I think those commits actually argue in favour of Tony's patch to remove
>> the special casing.  Is it really useful to create dma pools with a NULL
>> device?

> dma_alloc_coherent() does appear to support a NULL dev, so it might make
> sense in theory.  But I can't find any in-tree callers that actually
> pass a NULL dev to dma_pool_create().  So for one of the dreaded (NULL
> device *) messages to show up, it would take both a new caller that
> passes a NULL dev to dma_pool_create() and a bug to cause the message to
> be printed.  Is that worth the special casing?

So, then you need to rephrase the commit message explaining this
("NULL device is wrong to pass in the first place... bla bla bla").

-- 
With Best Regards,
Andy Shevchenko