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Date: Thu, 18 Jul 2024 16:26:13 +0300
From: Leon Romanovsky <leon@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Robin Murphy <robin.murphy@arm.com>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Easwar Hariharan <eahariha@linux.microsoft.com>,
	linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
	Jason Gunthorpe <jgg@nvidia.com>
Subject: Re: [PATCH v2 2/2] dma: add IOMMU static calls with clear default ops
Message-ID: <20240718132613.GA1265781@unreal>
References: <cover.1721219730.git.leon@kernel.org>
 <dd34bf3ecef252b4910d70aa21ff5273b5e8b19b.1721219730.git.leon@kernel.org>
 <20240718034854.GA31912@lst.de>
 <20240718070406.GK5630@unreal>
 <20240718123038.GA27055@lst.de>
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In-Reply-To: <20240718123038.GA27055@lst.de>

On Thu, Jul 18, 2024 at 02:30:38PM +0200, Christoph Hellwig wrote:
> On Thu, Jul 18, 2024 at 10:04:06AM +0300, Leon Romanovsky wrote:
> > Whom should I add?
> 
> Greg as the device model maintainer.

No problem, I will add him to the next version.

> 
> > > The normal style would be to move the ifdefs outside the helper
> > > function.
> > 
> > I think you are talking about the style of functions declarations in
> > header files. This function is inside c-file and it is much easier
> > to write it this way. 
> 
> But also much harder to read, which will happen much more often.

I'll change.

> 
> > > >  #ifdef CONFIG_DMA_OPS_BYPASS
> > > > +	WARN_ON_ONCE(dev->dma_ops_bypass && dma_is_default_iommu(dev));
> > > >  	if (dev->dma_ops_bypass)
> > > 
> > > Let's skip this and think about it if we ever use the bypass for
> > > something that is not powerpc with it's own dma ops.
> > 
> > I wanted to catch misconfigurations, but I can remove it. Is this what
> > you are suggesting?
> > 
> >   126 static bool dma_go_direct(struct device *dev, dma_addr_t mask, 
> >   127                 const struct dma_map_ops *ops)                
> >   128 {                                                            
> >   129         if (likely(!ops && !dma_is_default_iommu(dev)))     
> >   130                 return true;                               
> >   131                                                           
> >   132         if (dma_is_default_iommu(dev))    
> >   133                 return false;
> 
> I'd go for:
> 
> 		if (use_dma_iommu(dev))
> 			return false;
> 		if (likely(!ops))
> 			return true;
> 		...
> 

I will change.

Thanks