linux-kernel - Re: [RFC v2 00/13] usb/mmc/power: Fix USB/LAN when TFTP booting

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Message-ID: <CAPDyKFqpoi03Egfuvd8qJXnn_+FBgPXAb7S4UvkxVs8BA+zwnA@mail.gmail.com>
Date:	Mon, 9 May 2016 09:46:40 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Rob Herring <robh@...nel.org>
Cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	linux-usb@...r.kernel.org, Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nel.org>, hverkuil@...all.nl,
	tjakobi@...h.uni-bielefeld.de,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [RFC v2 00/13] usb/mmc/power: Fix USB/LAN when TFTP booting

On 6 May 2016 at 00:42, Rob Herring <robh@...nel.org> wrote:
> On Thu, May 05, 2016 at 02:34:13PM +0200, Krzysztof Kozlowski wrote:
>> Hi,
>>
>> This is a different, second try to fix usb3503+lan on Odroid U3 board
>> if it was initialized by bootloader (e.g. for TFTP boot).
>>
>> First version:
>> http://www.spinics.net/lists/linux-usb/msg140042.html
>>
>>
>> Problem
>> =======
>> When Odroid U3 (usb3503 + smsc95xx + max77686) boots from network (TFTP),
>> the usb3503 and LAN smsc95xx do not show up in "lsusb". Hard-reset
>> is required, e.g. by suspend to RAM. The actual TFTP boot does
>> not have to happen. Just "usb start" from U-Boot is sufficient.
>>
>> From the schematics, the regulator is a supply only to LAN, however
>> without toggling it off/on, the usb3503 hub won appear neither.
>>
>>
>> Solution
>> ========
>> This is very similar to the MMC pwrseq behavior so the idea is to:
>> 1. Move MMC pwrseq drivers to generic place,
>
> You can do that, but I'm going to NAK any use of pwrseq bindings outside
> of MMC. I think it is the wrong way to do things. The DT should describe

Huh, I didn't know that was your view of the mmc pwrseq bindings. Why
didn't you NAK them before?

> the devices. If they happen to be "simple" then the core can walk the
> tree and do any setup. For example, look for "reset-gpios" and toggle
> that GPIO. There is no need for a special node.
>
>> 2. Extend the pwrseq-simple with regulator toggling,
>> 3. Add support to USB hub and port core for pwrseq,
>
> We discussed this for USB already[1] and is why we defined how to add
> USB child devices. The idea is not to add pwrseq to that.

I am not familiar with the USB discussion.

Still, let me give you some more background to the mmc pwrseq. The
idea from the mmc pwrseq bindings comes from the power-domain DT
bindings, as I thought these things were a bit related.
In both cases they are not directly a property of the device, but more
describing a HW dependency to allow the device to work.

One could probably use a child node instead of a phandle, but that
wasn't chosen back then. Of course you are the DT expert, but could
you perhaps tell me why a child node is better for cases like this?

>
> Rob
>
> [1] http://www.spinics.net/lists/linux-usb/msg134082.html

Kind regards
Uffe