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

From: Krzysztof Kozlowski <k.kozlowski@samsung.com>
To: Rob Herring <robh@kernel.org>, hzpeterchen@gmail.com
Cc: devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org, linux-mmc@vger.kernel.org,
	linux-pm@vger.kernel.org, linux-usb@vger.kernel.org,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Sebastian Reichel <sre@kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Mark Brown <broonie@kernel.org>,
	hverkuil@xs4all.nl, tjakobi@math.uni-bielefeld.de,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	m.szyprowski@samsung.com
Subject: Re: [RFC v2 00/13] usb/mmc/power: Fix USB/LAN when TFTP booting
Date: Fri, 06 May 2016 08:10:38 +0200	[thread overview]
Message-ID: <572C355E.7090008@samsung.com> (raw)
In-Reply-To: <20160505224240.GA31429@rob-hp-laptop>

On 05/06/2016 12:42 AM, 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.

Okay, I got it, no node for pwrseq but parse device properties. In case
of reset-gpios it seems quite obvious but also actively used:
$ git grep reset-gpios arch/arm/boot/dts | wc -l
142

Definitely pwrseq shouldn't add itself to all of these devices.

My questions would be then:
1. An additional pwrseq compatible for device is acceptable?
2. How would you name the regulator? We shouldn't toggle off/on every
regulator but probably only some specific ones.

> 
>> 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.

Yes, I left it for next iteration because it would require much more
changes in USB core. As for now, these bindings are useless for USB
devices which are not yet enumerated (because power sequence has to be
done on them). Making use of these bindings would be a next step... Just
let me do it one step a time.

Best regards,
Krzysztof

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