linux-kernel - Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

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Date:	Wed, 27 Apr 2016 20:08:16 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Felipe Balbi <balbi@...nel.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Catalin Marinas <catalin.marinas@....com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	linux-usb@...r.kernel.org, Sekhar Nori <nsekhar@...com>,
	linux-kernel@...r.kernel.org,
	David Fisher <david.fisher1@...opsys.com>,
	"Thang Q. Nguyen" <tqnguyen@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

On Wednesday 27 April 2016 13:59:13 Alan Stern wrote:
> On Wed, 27 Apr 2016, Arnd Bergmann wrote:
> 
> > I've looked at the usb HCD code now and see this:
> > 
> > struct usb_hcd *usb_create_shared_hcd(const struct hc_driver *driver,
> >                 struct device *dev, const char *bus_name,
> >                 struct usb_hcd *primary_hcd)
> > {
> >       ...
> >         hcd->self.controller = dev;
> >         hcd->self.uses_dma = (dev->dma_mask != NULL);
> >       ...
> > }
> > 
> > What I think we need to do here is ensure that the device that gets
> > passed here and assigned to hcd->self.controller is the actual DMA
> > master device, i.e. the pci_device or platform_device that was created
> > from outside of the xhci stack. This is after all the pointer that
> > gets passed into all the dma_map_*/dma_sync_*/dma_alloc_*/...
> > functions.
> 
> It would be better to add a new field, since self.controller is also
> used for lots of other purposes.  Something like hcd->self.dma_dev.
> 

Ok, fair enough. I only took a brief look and all uses I found were
either for the DMA mapping API or some printk logging.

	Arnd