linux-kernel - Re: [PATCH 2/3] usb: dwc3: add Fujitsu Specific Glue layer

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Date:	Mon, 05 Jan 2015 16:28:34 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	balbi@...com
Cc:	Sneeker Yeh <sneeker.yeh@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Grant Likely <grant.likely@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Paul Bolle <pebolle@...cali.nl>,
	Hans de Goede <hdegoede@...hat.com>,
	Thomas Pugliese <thomas.pugliese@...il.com>,
	David Mosberger <davidm@...uge.net>,
	Peter Griffin <peter.griffin@...aro.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Andrew Bresticker <abrestic@...omium.org>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
	Andy Green <andy.green@...aro.org>,
	Jassi Brar <jaswinder.singh@...aro.org>,
	Sneeker Yeh <Sneeker.Yeh@...fujitsu.com>
Subject: Re: [PATCH 2/3] usb: dwc3: add Fujitsu Specific Glue layer

On Friday 02 January 2015 19:21:28 Felipe Balbi wrote:
> 
> On Tue, Dec 30, 2014 at 11:12:51AM +0100, Arnd Bergmann wrote:
> > On Monday 29 December 2014 01:52:04 Sneeker Yeh wrote:
> > > > > +static int dwc3_mb86s70_remove_child(struct device *dev, void *unused)
> > > > > +{
> > > > > +     struct platform_device *pdev = to_platform_device(dev);
> > > > > +
> > > > > +     of_device_unregister(pdev);
> > > > > +
> > > > > +     return 0;
> > > > > +}
> > > > > +
> > > > > +static u64 dwc3_mb86s70_dma_mask = DMA_BIT_MASK(32);
> > > >
> > > > why ? Use dma_coerce_mask_and_coherent().
> > > >
> > > 
> > > okay.
> > 
> > Actually that is still wrong: we use dma_coerce_mask_and_coherent() to
> > annotate drivers that have traditionally been forcing their own dma mask
> > by some other means and that need to be changed to something proper (after
> > finding out why they did it in the first place).
> > 
> > Since this is about a child device, the correct interface is to use
> > platform_device_register_full().
> 
> no, that's wrong. He's essentially fixing the default set by OF core,
> which is always 32-bits anyway, so this can actually be removed. Your
> suggestion would just make it worse.

Ah, so this was for a device that gets probed from DT? Yes, then no
change is needed here at all.

Note that I'm working on a patch set to change the DT initialization to
be a little smarter about the mask. Specifically any device whose parent
has a smaller dma-ranges window than 4GB needs to start out with the
smaller mask, and the dma_set_mask function that is called to allow 64-bit
DMA on a device will check if the bus can actually support it.

	Arnd
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