netdev - Re: [Linaro-acpi] [V2 PATCH 2/5] arm64 : Introduce support for ACPI

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Date:	Tue, 05 May 2015 20:02:53 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Tom Lendacky <thomas.lendacky@....com>
Cc:	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	linaro-acpi@...ts.linaro.org, rjw@...ysocki.net,
	herbert@...dor.apana.org.au, catalin.marinas@....com,
	will.deacon@....com, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-crypto@...r.kernel.org,
	netdev@...r.kernel.org, davem@...emloft.net,
	linux-arm-kernel@...ts.infradead.org, lenb@...nel.org
Subject: Re: [Linaro-acpi] [V2 PATCH 2/5] arm64 : Introduce support for ACPI _CCA object

On Tuesday 05 May 2015 11:24:03 Tom Lendacky wrote:
> On 05/05/2015 11:13 AM, Suravee Suthikulanit wrote:
> > On 5/5/2015 11:12 AM, Arnd Bergmann wrote:
> >> On Tuesday 05 May 2015 11:09:38 Suravee Suthikulanit wrote:
> >>>
> >>> However, codes in several places are making use of dma_map_ops without
> >>> checking if the ops are NULL (i.e.
> >>> include/asm-generic/dma-mapping-common.h and in arch-specific
> >>> implementation). If setting it to NULL is what we are planning to
> >>> support, we would need to scrub the current code to put NULL check.
> >>> Also, would you consider if that is safe to do going forward?
> >>>
> >>>
> >>
> >> I mean the dma_mask pointer, not dma_map_ops.
> 
> Except a lot of drivers will actually set the dma_mask pointer during
> probe (usually by setting dev->dma_mask = &dev->coherent_dma_mask or by
> calling dma_coerce_mask_and_coherent).  So I think the dummy_dma_ops
> might be the safest way to go.

Those drivers are broken already, I don't think we should worry about
them. Let's just fix them properly when we run into problems with them.

Basically any use of dma_coerce_mask_and_coherent() is an annotation
for a bug where a driver used to set dev->dma_mask = &dev->coherent_dma_mask
manually.

	Arnd
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