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

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Date:	Wed, 31 Jul 2013 17:29:40 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
CC:	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 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.
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