linux-kernel - Re: [PATCH kernel v3 1/2] dma: Allow mixing bypass and mapped DMA operation

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Message-ID: <2d9957af-23b6-943f-faac-fc7607b6e250@ozlabs.ru>
Date:   Thu, 29 Oct 2020 10:15:13 +1100
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Christoph Hellwig <hch@....de>
Cc:     linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH kernel v3 1/2] dma: Allow mixing bypass and mapped DMA
 operation



On 29/10/2020 04:22, Christoph Hellwig wrote:
> On Wed, Oct 28, 2020 at 06:00:29PM +1100, Alexey Kardashevskiy wrote:
>> At the moment we allow bypassing DMA ops only when we can do this for
>> the entire RAM. However there are configs with mixed type memory
>> where we could still allow bypassing IOMMU in most cases;
>> POWERPC with persistent memory is one example.
>>
>> This adds an arch hook to determine where bypass can still work and
>> we invoke direct DMA API. The following patch checks the bus limit
>> on POWERPC to allow or disallow direct mapping.
>>
>> This adds a CONFIG_ARCH_HAS_DMA_SET_MASK config option to make arch_xxxx
>> hooks no-op by default.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
>> ---
>>   kernel/dma/mapping.c | 24 ++++++++++++++++++++----
>>   kernel/dma/Kconfig   |  4 ++++
>>   2 files changed, 24 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
>> index 51bb8fa8eb89..a0bc9eb876ed 100644
>> --- a/kernel/dma/mapping.c
>> +++ b/kernel/dma/mapping.c
>> @@ -137,6 +137,18 @@ static inline bool dma_map_direct(struct device *dev,
>>   	return dma_go_direct(dev, *dev->dma_mask, ops);
>>   }
>>   
>> +#ifdef CONFIG_ARCH_HAS_DMA_MAP_DIRECT
>> +bool arch_dma_map_page_direct(struct device *dev, phys_addr_t addr);
>> +bool arch_dma_unmap_page_direct(struct device *dev, dma_addr_t dma_handle);
>> +bool arch_dma_map_sg_direct(struct device *dev, struct scatterlist *sg, int nents);
>> +bool arch_dma_unmap_sg_direct(struct device *dev, struct scatterlist *sg, int nents);
>> +#else
>> +#define arch_dma_map_page_direct(d, a) (0)
>> +#define arch_dma_unmap_page_direct(d, a) (0)
>> +#define arch_dma_map_sg_direct(d, s, n) (0)
>> +#define arch_dma_unmap_sg_direct(d, s, n) (0)
>> +#endif
> 
> A bunch of overly long lines here.  Except for that this looks ok to me.
> If you want me to queue up the series I can just fix it up.

I thought 100 is the new limit since 
https://lkml.org/lkml/2020/5/29/1038 (yeah that mentioned some Christoph 
:) ) and having these multiline does not make a huge difference but feel 
free fixing them up.

Are you going to take both patches? Do you need mpe's ack? Thanks,


-- 
Alexey