linux-kernel - Re: [RFT PATCH 2/2] Revert "usb: dwc2: Fix probe problem on bcm2835"

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Date:	Sat, 19 Mar 2016 00:14:49 +0100 (CET)
From:	Stefan Wahren <stefan.wahren@...e.com>
To:	John Youn <John.Youn@...opsys.com>,
	Doug Anderson <dianders@...omium.org>,
	Eric Anholt <eric@...olt.net>,
	Martin Sperl <kernel@...tin.sperl.org>
Cc:	Michael Niewoehner <linux@...ewoehner.de>,
	Tao Huang <huangtao@...k-chips.com>,
	Julius Werner <jwerner@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Caesar Wang <caesar.upstream@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Felipe Balbi <balbi@...nel.org>,
	Remi Pommarel <repk@...plefau.lt>
Subject: Re: [RFT PATCH 2/2] Revert "usb: dwc2: Fix probe problem on
 bcm2835"

Hi Eric,
hi Martin,

> John Youn <John.Youn@...opsys.com> hat am 16. März 2016 um 19:28 geschrieben:
>
>
> On 3/10/2016 11:14 AM, John Youn wrote:
> > On 3/9/2016 11:06 AM, Doug Anderson wrote:
> >> Stefan,
> >>
> >> On Wed, Mar 9, 2016 at 11:01 AM, Stefan Wahren <stefan.wahren@...e.com>
> >> wrote:
> >>>
> >>>> Doug Anderson <dianders@...omium.org> hat am 7. März 2016 um 22:30
> >>>> geschrieben:
> >>>>
> >>>>
> >>>> Stefan,
> >>>>
> >>>> On Mon, Mar 7, 2016 at 10:40 AM, Stefan Wahren <stefan.wahren@...e.com>
> >>>> wrote:
> >>>>> Hi Doug,
> >>>>>
> >>>>>> Douglas Anderson <dianders@...omium.org> hat am 4. März 2016 um 19:23
> >>>>>> geschrieben:
> >>>>>>
> >>>>>>
> >>>>>> This reverts commit 192cb07f7928 ("usb: dwc2: Fix probe problem on
> >>>>>> bcm2835") now that we've found the root cause. See the change
> >>>>>> titled ("usb: dwc2: Add a 10 ms delay to dwc2_core_reset()").
> >>>>>
> >>>>> adding a delay of 10 ms after a core reset might be a idea, but applying
> >>>>> both
> >>>>> patches breaks USB support on RPi :-(
> >>>>>
> >>>>> I'm getting the wrong register values ...
> >>>>
> >>>> Ugh. :(
> >>>>
> >>>> Just out of curiosity, if you loop and time long it takes for the
> >>>> registers to get to the right state after reset, what do you get?
> >>>> AKA, pick:
> >>>>
> >>>> https://chromium-review.googlesource.com/331260
> >>>>
> >>>> ...and let me know what it prints out.
> >>>
> >>> On my Raspberry Pi B i get the following:
> >>>
> >>> [ 2.084411] dwc2 20980000.usb: mapped PA 20980000 to VA cc880000
> >>> [ 2.084461] dwc2 20980000.usb: cannot get otg clock
> >>> [ 2.084549] dwc2 20980000.usb: registering common handler for irq33
> >>> [ 2.084713] dwc2 20980000.usb: Configuration mismatch. dr_mode forced to
> >>> host
> >>> [ 2.153965] dwc2 20980000.usb: Waited 49996 us, 0x00201000 => 0x01001000,
> >>> 0x00000000 => 0x02002000
> >>> [ 2.174930] dwc2 20980000.usb: Forcing mode to host
> >>>
> >>> So i changed the delay in patch #1 to msleep(50) and then both patches
> >>> work like
> >>> a charm.
> >>
> >> Great news! :-)
> >>
> >> John: it's pretty clear that there's something taking almost exactly
> >> 10ms on my system and almost exactly 50ms on Stefan's system. Is
> >> there some register we could poll to see when this process is done?
> >> ...or can we look at the dwc2 revision number / feature register and
> >> detect how long to delay?
> >>
> >
> > Hi Doug,
> >
> > I'll have to ask around to see if anyone knows about this. And I'll
> > run some tests on the platforms I have available to me as well.
> >
>
> There's still nothing definitive on our end as to why this is
> happening. Also I don't think there is any other way to poll the
> reset. Our hardware engineers asked for some more information to look
> into it further. Doug, Stefan, Caesar, and anyone else with a related
> platform, do you know the answers to the following:
>
> 1. What is the AHB Clock frequency? Is the AHB Clock gated during
> Reset?
>
> 2. Also is the PHY clock stopped during the reset or is the PHY PLL
> lock times high in the order of ms?
>
> 3. In these cases, is the PHY actually an FS Transceiver and not a
> UTMI/ULPI PHY?

are you able to answer these questions 1 - 3 for BCM2835? I don't want to say
something wrong here.

>
> 4. Which version of the controller is being used in these cases?

@John: The BCM2835 has version 2.80a

Regards
Stefan

>
> Regards,
> John