linux-kernel - Re: [PATCH RESEND] dma-mapping: tidy up dma

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Message-ID: <CAO_48GHXaNE4m5TErg0=nkDZrvi65mp8u4h7ao011OL4mhSDUw@mail.gmail.com>
Date:	Thu, 22 Jan 2015 09:15:08 +0530
From:	Sumit Semwal <sumit.semwal@...aro.org>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	Robin Murphy <robin.murphy@....com>,
	Will Deacon <will.deacon@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>, joro@...tes.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	iommu@...ts.linux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RESEND] dma-mapping: tidy up dma_parms default handling

Hi Robin,

On 13 January 2015 at 16:49, Marek Szyprowski <m.szyprowski@...sung.com> wrote:
> Hello,
>
> On 2015-01-09 17:56, Robin Murphy wrote:
>>
>> Many DMA controllers and other devices set max_segment_size to
>> indicate their scatter-gather capability, but have no interest in
>> segment_boundary_mask. However, the existence of a dma_parms structure
>> precludes the use of any default value, leaving them as zeros (assuming
>> a properly kzalloc'ed structure). If a well-behaved IOMMU (or SWIOTLB)
>> then tries to respect this by ensuring a mapped segment does not cross
>> a zero-byte boundary, hilarity ensues.
>>
>> Since zero is a nonsensical value for either parameter, treat it as an
>> indicator for "default", as might be expected. In the process, clean up
>> a bit by replacing the bare constants with slightly more meaningful
>> macros and removing the superfluous "else" statements.
>>
>> Signed-off-by: Robin Murphy <robin.murphy@....com>
>
>
> Acked-by: Marek Szyprowski <m.szyprowski@...sung.com>

Please feel free to add my
Reviewed-by: Sumit Semwal <sumit.semwal@...aro.org>
>
>> ---
>>
>> Hi, various maintainers from Git logs ;)
>>
>> This one's a bit tricky to find a home for - I think technically it's
>> probably an IOMMU patch, but then the long-underlying problem doesn't
>> seem to have blown up anything until arm64, and my motivation is to
>> make bits of Juno work, which seems to nudge it towards arm64/arm-soc
>> territory. Could anyone suggest which tree is most appropriate?
>>
>> Thanks,
>> Robin.
>>
>>
>>   include/linux/dma-mapping.h | 17 ++++++++++-------
>>   1 file changed, 10 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
>> index c3007cb..99ba736 100644
>> --- a/include/linux/dma-mapping.h
>> +++ b/include/linux/dma-mapping.h
>> @@ -141,7 +141,9 @@ static inline void arch_teardown_dma_ops(struct device
>> *dev) { }
>>     static inline unsigned int dma_get_max_seg_size(struct device *dev)
>>   {
>> -       return dev->dma_parms ? dev->dma_parms->max_segment_size : 65536;
>> +       if (dev->dma_parms && dev->dma_parms->max_segment_size)
>> +               return dev->dma_parms->max_segment_size;
>> +       return SZ_64K;
>>   }
>>     static inline unsigned int dma_set_max_seg_size(struct device *dev,
>> @@ -150,14 +152,15 @@ static inline unsigned int
>> dma_set_max_seg_size(struct device *dev,
>>         if (dev->dma_parms) {
>>                 dev->dma_parms->max_segment_size = size;
>>                 return 0;
>> -       } else
>> -               return -EIO;
>> +       }
>> +       return -EIO;
>>   }
>>     static inline unsigned long dma_get_seg_boundary(struct device *dev)
>>   {
>> -       return dev->dma_parms ?
>> -               dev->dma_parms->segment_boundary_mask : 0xffffffff;
>> +       if (dev->dma_parms && dev->dma_parms->segment_boundary_mask)
>> +               return dev->dma_parms->segment_boundary_mask;
>> +       return DMA_BIT_MASK(32);
>>   }
>>     static inline int dma_set_seg_boundary(struct device *dev, unsigned
>> long mask)
>> @@ -165,8 +168,8 @@ static inline int dma_set_seg_boundary(struct device
>> *dev, unsigned long mask)
>>         if (dev->dma_parms) {
>>                 dev->dma_parms->segment_boundary_mask = mask;
>>                 return 0;
>> -       } else
>> -               return -EIO;
>> +       }
>> +       return -EIO;
>>   }
>>     #ifndef dma_max_pfn
>
>
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>
>
> --
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-- 
Thanks and regards,

Sumit Semwal
Kernel Team Lead - Linaro Mobile Group
Linaro.org │ Open source software for ARM SoCs
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