linux-kernel - Re: [PATCH kernel v2 1/2] dma: Allow mixing bypass and normal IOMMU operation

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Message-ID: <20201028172106.GA10015@lst.de>
Date:   Wed, 28 Oct 2020 18:21:06 +0100
From:   Christoph Hellwig <hch@....de>
To:     Alexey Kardashevskiy <aik@...abs.ru>
Cc:     Christoph Hellwig <hch@....de>, 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 v2 1/2] dma: Allow mixing bypass and normal
 IOMMU operation

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.