linux-kernel - Re: [RFT 0/3] usb: usb3503: Fix probing on Arndale board (missing phy)

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Message-ID: <561638ED.1060503@osg.samsung.com>
Date:	Thu, 8 Oct 2015 11:35:41 +0200
From:	Javier Martinez Canillas <javier@....samsung.com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Chen <peter.chen@...escale.com>,
	Ben Gamari <ben@...rt-cactus.org>,
	Wolfram Sang <wsa@...-dreams.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Kukjin Kim <kgene@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org
Cc:	Kevin Hilman <khilman@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	riku.voipio@...aro.org
Subject: Re: [RFT 0/3] usb: usb3503: Fix probing on Arndale board (missing
 phy)

Hello,

On 10/08/2015 08:23 AM, Marek Szyprowski wrote:
> Hello,
> 
> On 2015-10-08 08:02, Krzysztof Kozlowski wrote:
>> On 07.10.2015 23:26, Marek Szyprowski wrote:
>>> Hello,
>>>
>>> On 2015-10-07 02:30, Krzysztof Kozlowski wrote:
>>>> Introduction
>>>> ============
>>>> This patchset tries to fix probing of usb3503 on Arndale board
>>>> if the Samsung PHY driver is probed later (or built as a module).
>>>>
>>>> *The patchset was not tested on Arndale board.*
>>>> I don't have that board. Please test it and say if the usb3503
>>>> deferred probe
>>>> works fine and the issue is solved.
>>>>
>>>> The patchset was tested on Odroid U3 board (which is different!)
>>>> in a simulated environment. It is not sufficient testing.
>>>>
>>>>
>>>> Difference
>>>> ==========
>>>> The usb3503 device driver can be used as a I2C device (on Odroid U3)
>>>> or as a platform device connected through phy (on Arndale). In the second
>>>> case the necessary phy reference has to be obtained and enabled.
>>>>
>>>> For some details please look also at thread [0][1].
>>>>
>>>> [0]
>>>> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-June/348524.html
>>>>
>>>> [1]
>>>> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-June/348875.html
>>>>
>>>>
>>> I'm not sure that this is the correct approach. usb3503 chip is simply
>>> connected
>>> to Exynos USB2 phy, so it visible on the USB bus. The real driver that
>>> controls USB2
>>> PHY is Exynos EHCI driver and USB3503 should not mess around it.
>> The ehci node (usb@...10000) has one port configured and it takes one
>> PHY reference (phy of id 1 - USB host). I can't see driver taking
>> reference to HSIC0 or HSIC1 phys... Since I cannot diagnose the error I
>> don't know what is really expected here.
> 
> It looks that EHCI in Exynos 5250 and 5420 still use old phy bindings. For
> the reference, see Exynos4 dts and exynos4412-odroidu3.dts to check how to enable
> more than one USB port (Odroid U3 has both HSIC ports enabled).
> 
>>
>>> In my opinion all that is needed in case of Arndale board is forcing
>>> reset of
>>> usb3503 chip after successful EHCI and USB2 PHY initialization (for some
>>> reason
>>> initialization of usb3503 chip must be done after usb host initialization).
>>> However I have no idea which driver should trigger this reset. Right now
>>> I didn't
>>> find any good solution for additional control for devices which are on
>>> autoprobed
>>> bus like usb.
>> The reset is done at the end of usb3503's probe. The question "why
>> usb3503 has to be initialized after EHCI and USB PHY" is still valid...
> 
> I remember that I saw some code to reset HSIC device after phy power on in case
> of HSIC-connected modem chip, so maybe this is somehow common for HSIC chips
> (which are some special case of 'embedded usb').
>

I also don't have an Arndale board and haven't followed the thread to closely
but I just wanted to mention that the ChromiumOS 3.8 tree has a workaround to
reset the HSIC phys:

https://chromium.googlesource.com/chromiumos/third_party/kernel/+/81685c447954a29d1098268776582457258dd98f%5E%21/

and later a "supports-hsicphy-reset" DT property was added to force the reset
per board instead of unconditionally:

https://chromium.googlesource.com/chromiumos/third_party/kernel/+/a4d1c1a223ffa1ed38a4257d0378ca70c6667be0%5E%21/

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America
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