linux-kernel - Re: [PATCH 2/2] ARM: dts: USB for Tegra114 Dalmore

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Date:	Thu, 15 Aug 2013 12:54:05 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Tuomas Tynkkynen <tuomas.tynkkynen@....fi>,
	Tuomas Tynkkynen <ttynkkynen@...dia.com>,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, Mikko Perttunen <mperttunen@...dia.com>
Subject: Re: [PATCH 2/2] ARM: dts: USB for Tegra114 Dalmore

On Wed, Jul 31, 2013 at 05:29:40PM -0600, Stephen Warren wrote:
> On 07/31/2013 04:20 PM, Sergei Shtylyov wrote:
> > On 08/01/2013 02:06 AM, Stephen Warren wrote:
> ...
> >>>     That's really horrible design.
> >>
> >> Yup. Both USB PHY and EHCI controller registers really are interleaved
> >> in one range.
> > 
> >    But the standard EHCI register space has no holes IIRC, so they can't
> > be really that much interleaved as you're describing (unless you have
> > some non-standard registers of course)...
> 
> Yes, there are certainly non-standard registers.
> 
> ...
> >>>     Don't they cause numerous resource conflicts while device nodes
> >>> being
> >>> instantiated as the platform devices?
> > 
> >> No; the driver knows that the HW is screwy and there's lots of
> >> register-range sharing going on, so it simply maps the registers, rather
> >> than reserving the physical address range and mapping it.
> > 
> >    Yes, it's clear that the driver should take special measures, I was
> > asking about the platform device creation phase. What do you see in
> > /proc/iomem?
> 
> The drivers don't request the memory region since doing so would cause
> conflicts. Hence, the regions don't show up in /proc/iomem.
> 
> This actually isn't that uncommon for DT-based drivers anyway; many use
> e.g. of_iomap() which IIRC just looks up the resource and maps it
> without registering the usage.

Not being uncommon isn't a good argument. The problem with doing this is
that it sets a bad example and makes it easier for others to do the same
thing. I can see that for some drivers providing a proper abstraction or
encapsulation might be more complicated than necessary. But I've also
seen this kind of shortcut taken quite often lately and especially often
in DT-based drivers.

Am I the only one concerned about this development?

Thierry

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