linux-kernel - Re: [PATCH] ARM: tegra: add device tree for SHIELD

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Date:	Tue, 25 Feb 2014 22:02:02 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Alexandre Courbot <acourbot@...dia.com>,
	Thierry Reding <thierry.reding@...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>,
	Russell King <linux@....linux.org.uk>
CC:	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: tegra: add device tree for SHIELD

On 02/25/2014 09:58 PM, Alexandre Courbot wrote:
> On 02/26/2014 07:38 AM, Stephen Warren wrote:
>> On 02/24/2014 07:13 PM, Alexandre Courbot wrote:
>>> On 02/25/2014 03:53 AM, Stephen Warren wrote:
>>>> On 02/24/2014 03:26 AM, Alexandre Courbot wrote:
>>>>> Add a device tree for NVIDIA SHIELD. The set of enabled features is
>>>>> still minimal with no display option (although HDMI should be easy
>>>>> to get to work) and USB requiring external power.
...
>>> For the Wifi chip, non-removable would be the correct setting
>>> hardware-wise, but there is a trap: the chip has its reset line asserted
>>> at boot-time, and you need to set GPIO 229 to de-assert it. Only after
>>> that will the device be detected on the SDIO bus. Since it lacks a CD
>>> line, it must be polled, hence the broken-cd property.
>>
>> How does that GPIO get manipulated right now? I assume you must be
>> manually configuring it via sysfs after boot or something? If so,
>> perhaps it's best to just leave out the WiFi node until it works
>> automatically.
> 
> The GPIO needs to be set from user-space, yes. But if we leave the Wifi
> node out, I'm concerned that wireless will not be usable at all,
> wouldn't it?

True, but if we have no representation of the device in DT that works
without manually enabling clocks and/or GPIOs, it's not a
complete/accurate representation of the HW, so it doesn't make sense to
add it to DT. Yes, I admit that sucks.

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