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Subject: Re: [PATCH kernel v2 1/2] dma: Allow mixing bypass and normal IOMMU
 operation
To:     Christoph Hellwig <hch@lst.de>
Cc:     linuxppc-dev@lists.ozlabs.org,
        Michael Ellerman <mpe@ellerman.id.au>,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
References: <20201027101841.96056-1-aik@ozlabs.ru>
 <20201027101841.96056-2-aik@ozlabs.ru> <20201027164858.GA30651@lst.de>
 <28147035-500d-f3cd-f283-257066343697@ozlabs.ru>
 <20201028172106.GA10015@lst.de>
From:   Alexey Kardashevskiy <aik@ozlabs.ru>
Message-ID: <f4420b19-05cd-5817-9ba4-8f6f166a7e5c@ozlabs.ru>
Date:   Thu, 29 Oct 2020 10:11:45 +1100
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On 29/10/2020 04:21, Christoph Hellwig wrote:
> On Wed, Oct 28, 2020 at 05:55:23PM +1100, Alexey Kardashevskiy wrote:
>>
>> It is passing an address of the end of the mapped area so passing a page
>> struct means passing page and offset which is an extra parameter and we do
>> not want to do anything with the page in those hooks anyway so I'd keep it
>> as is.
>>
>>
>>> and
>>>      maybe even hide the dma_map_direct inside it.
>>
>> Call dma_map_direct() from arch_dma_map_page_direct() if
>> arch_dma_map_page_direct() is defined? Seems suboptimal as it is going to
>> be bypass=true in most cases and we save one call by avoiding calling
>> arch_dma_map_page_direct(). Unless I missed something?
> 
> C does not even evaluate the right hand side of a || expression if the
> left hand evaluates to true.

Right, this is what I meant. dma_map_direct() is inline and fast so I 
did not want it inside the arch hook which is not inline.


-- 
Alexey