linux-kernel - Re: [PATCH RFT RESEND linux-next] mips: dma-mapping: support debug_dma_mapping

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Date:	Fri, 26 Oct 2012 13:07:02 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	shuah.khan@...com
CC:	ralf@...ux-mips.org, kyungmin.park@...sung.com, arnd@...db.de,
	andrzej.p@...sung.com, m.szyprowski@...sung.com,
	linux-mips@...ux-mips.org, LKML <linux-kernel@...r.kernel.org>,
	shuahkhan@...il.com
Subject: Re: [PATCH RFT RESEND linux-next] mips: dma-mapping: support debug_dma_mapping_error

On 10/26/2012 10:06 AM, Shuah Khan wrote:
> On Fri, 2012-10-26 at 09:45 -0700, David Daney wrote:
>> On 10/26/2012 09:01 AM, Shuah Khan wrote:
>>> Add support for debug_dma_mapping_error() call to avoid warning from
>>> debug_dma_unmap() interface when it checks for mapping error checked
>>> status. Without this patch, device driver failed to check map error
>>> warning is generated.
>>>
>>> Signed-off-by: Shuah Khan <shuah.khan@...com>
>>> ---
>>>    arch/mips/include/asm/dma-mapping.h |    2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/arch/mips/include/asm/dma-mapping.h b/arch/mips/include/asm/dma-mapping.h
>>> index be39a12..006b43e 100644
>>> --- a/arch/mips/include/asm/dma-mapping.h
>>> +++ b/arch/mips/include/asm/dma-mapping.h
>>> @@ -40,6 +40,8 @@ static inline int dma_supported(struct device *dev, u64 mask)
>>>    static inline int dma_mapping_error(struct device *dev, u64 mask)
>>>    {
>>>    	struct dma_map_ops *ops = get_dma_ops(dev);
>>> +
>>> +	debug_dma_mapping_error(dev, mask);
>>>    	return ops->mapping_error(dev, mask);
>>>    }
>>>
>>>
>>
>> Although this is a start, I don't think it is sufficient.
>>
>> As far as I can tell, there are many missing calls to debug_dma_*() in
>> the various MIPS commone and sub-architecture DMA code.
>>
>> Really you (or someone) needs to look at *all* the functions in
>> arch/mips/asm/dma-mapping.h, and arch/mips/mm/dma-default.c and find
>> places missing a debug_dma_*().
>
> Is it correct to assume that this patch is not needed on MIPS until
> debug_dma interfaces get added to MIPS common and sub-architecture DMA
> code.

No, you have a false predicate here.

debug_dma_* *is* already mostly added.  The problem is that it is 
incomplete.  That is the nature of the problem.  Your patch makes it 
slightly better, but doesn't fully fix the problems.


>
> When I didn't see dma_map_page() in arch/mips/include/asm/dma-mapping.h
> defined, and just an extern, I incorrectly assumed, it is getting picked
> up from <asm-generic/dma-mapping-common.h>, hence the need for this
> patch in the first place.
>
> -- Shuah
>
>
>

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