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

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Date:	Fri, 6 May 2016 13:44:59 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Rob Herring <robh@...nel.org>
Cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-mmc@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-usb@...r.kernel.org,
	Ulf Hansson <ulf.hansson@...aro.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>,
	m.szyprowski@...sung.com
Subject: Re: [RFC v2 00/13] usb/mmc/power: Fix USB/LAN when TFTP booting

On Thu, May 05, 2016 at 05:42:40PM -0500, Rob Herring 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 
> 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.
> 

Oh, I am doing the same thing like this patch set doing. Then, how can
we let things be generic like you mention at [1] if without common
pwrseq driver/library? The properties like "reset-gpios" under
USB child node seems can only be handled by USB driver.

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

[1] http://www.spinics.net/lists/linux-usb/msg137312.html

-- 

Best Regards,
Peter Chen