linux-kernel - Re: Bug: shared usb dt document is incorrect

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Date:	Wed, 29 Jul 2015 10:29:08 -0700
From:	Tim Bird <tim.bird@...ymobile.com>
To:	Rob Herring <robherring2@...il.com>
CC:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Chen <Peter.Chen@...escale.com>,
	Linux USB List <linux-usb@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Andersson, Björn" 
	<Bjorn.Andersson@...ymobile.com>
Subject: Re: Bug: shared usb dt document is incorrect



On 07/28/2015 07:54 PM, Rob Herring wrote:
> On Tue, Jul 28, 2015 at 8:06 PM, Tim Bird <tim.bird@...ymobile.com> wrote:
>> Antoine and Rob,
>>
>> I was just doing some testing with USB on a Qualcomm SoC.
>>
>> I followed the instructions in the binding document:
>> Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt
>>
>> which has a compatible for "qcom,ci-hdrc", and is, in general,
>> for chipidea-based USB controllers.
>>
>> It says in the document that the property usb-phy is deprecated, and to
>> use phys and phy-names instead.  However, the Qualcomm
>> driver for this still uses usb-phy.  That driver is in:
>> drivers/usb/chipidea/ci_hdrc_msm.c
> 
> Deprecated means it still exists in the wild and should be maintained,
> but don't use it for new dts files.
OK.  But for the Qualcomm driver, the new binding doesn't work (see below).
Since the binding doc specifically says: 'Use "phys" instead [of "usb-phy"].',
it is wrong as currently written, for this controller/phy combination.

>> I'm guessing I should update the Qualcomm driver to use
>> phys and phy-names, but wanted to check with you-all to
>> verify that this is the preferred method of getting
>> phys by phandle now.  It's either change the driver
>> or make an exception in the binding document, I believe.
> 
> That would be fine along with updating the dts files, but the doc
> should remain for some time.

Does this mean I should try phys/phy-names, and if that doesn't work
try usb-phy, for backwards compatibility?

>> I presume I should be changing devm_usb_get_phy_by_phandle()
>> to of_phy_get(), but let me know if there's more to it than that.
> 
> devm_phy_get actually. The driver already supports it. See
> ci_hdrc_probe in core.c.

In my case the probe that is running is ci_hdrc_msm_probe(), in ci_hdrc_msm.c
This probe uses devm_usb_get_phy_by_phandle(..."usb-phy").  If I specify phys/phy-names
in my dts, the probe fails silently - leading ultimately to USB not working.
If I specify "usb-phy" in my dts, everything works. In this case, that property
is NOT deprecated.  It's the only one that works.

I don't understand what's going on with the different probe routines and how the
SoC-specific parts interact with the core.  I just know that the kernel behaviour
and the binding doc don't match, and I'd like to help fix it if I can.

Thanks for your patience while I try to understand this issue.
 -- Tim
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