From mboxrd@z Thu Jan  1 00:00:00 1970
From: arnd@arndb.de (Arnd Bergmann)
Date: Wed, 27 Apr 2016 18:04:27 +0200
Subject: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev
In-Reply-To: <20160427155019.GE20646@e104818-lin.cambridge.arm.com>
References: <1461612094-30939-1-git-send-email-grygorii.strashko@ti.com>
 <9452408.uEOOA4q1YW@wuerfel>
 <20160427155019.GE20646@e104818-lin.cambridge.arm.com>
Message-ID: <4985498.GT33RtioOA@wuerfel>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wednesday 27 April 2016 16:50:19 Catalin Marinas wrote:
> On Wed, Apr 27, 2016 at 04:11:17PM +0200, Arnd Bergmann wrote:
> > On Wednesday 27 April 2016 14:59:00 Catalin Marinas wrote:
> > > 
> > > I would be in favour of a dma_inherit() function as well. We could hack
> > > something up in the arch code (like below) but I would rather prefer an
> > > explicit dma_inherit() call by drivers creating such devices.
> > > 
> > > diff --git a/arch/arm64/include/asm/dma-mapping.h b/arch/arm64/include/asm/dma-mapping.h
> > > index ba437f090a74..ea6fb9b0e8fa 100644
> > > --- a/arch/arm64/include/asm/dma-mapping.h
> > > +++ b/arch/arm64/include/asm/dma-mapping.h
> > > @@ -29,8 +29,11 @@ extern struct dma_map_ops dummy_dma_ops;
> > >  
> > >  static inline struct dma_map_ops *__generic_dma_ops(struct device *dev)
> > >  {
> > > -       if (dev && dev->archdata.dma_ops)
> > > -               return dev->archdata.dma_ops;
> > > +       while (dev) {
> > > +               if (dev->archdata.dma_ops)
> > > +                       return dev->archdata.dma_ops;
> > > +               dev = dev->parent;
> > > +       }
> > 
> > I think this would be a very bad idea: we don't want to have random
> > devices be able to perform DMA just because their parent devices
> > have been set up that way.
> 
> I agree, it's a big hack. It would be nice to have a simpler way to do
> this in driver code rather than explicitly calling
> of_dma_configure/arch_setup_dma_ops as per the original patch in this
> thread.
> 


I haven't followed the entire discussion, but what's wrong with passing
around a pointer to a 'struct device *hwdev' that represents the physical
device that does the DMA?

	Arnd