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

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Date:	Sat, 19 Mar 2016 13:09:09 +0100 (CET)
From:	Stefan Wahren <stefan.wahren@...e.com>
To:	Martin Sperl <kernel@...tin.sperl.org>
Cc:	Michael Niewoehner <linux@...ewoehner.de>,
	Tao Huang <huangtao@...k-chips.com>,
	John Youn <John.Youn@...opsys.com>,
	Julius Werner <jwerner@...omium.org>,
	Eric Anholt <eric@...olt.net>,
	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>,
	Doug Anderson <dianders@...omium.org>,
	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,

> Martin Sperl <kernel@...tin.sperl.org> hat am 19. März 2016 um 11:10
> geschrieben:
>
>
> > On 19.03.2016, at 10:52, Stefan Wahren <stefan.wahren@...e.com> wrote:
> >
> > Hi,
> >
> >> Martin Sperl <kernel@...tin.sperl.org> hat am 19. März 2016 um 08:44
> >> geschrieben:
> >>
> >>
> >>
> >>> On 19.03.2016, at 03:17, Eric Anholt <eric@...olt.net> wrote:
> >>>
> >>> Stefan Wahren <stefan.wahren@...e.com> writes:
> >>>
> >>>> 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:
> >>>>>>>
> >>>>>>> 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?
> >>>>>>>
> >>
> >> Maybe this difference is related to overclocking settings in the firmware?
> >>
> >>>>>
> >>>>> 1. What is the AHB Clock frequency? Is the AHB Clock gated during
> >>>>> Reset?
> >>>
> >>> Low confidence here as I'm tracing lines across a ton of modules, but it
> >>> looks like it comes from the USB AXI clock in peri_image, which is a
> >>> gate on the normal 250Mhz APB clock, but nothing should be touching that
> >>> gate register as part of USB reset as far as I know.
> >>>
> >> Isn’t it possible that this clock (probably BCM2835_CLOCK_VPU) is
> >> changed by the firmware due to overclocking settings in /boot/config.txt?
> >
> > i don't use any overclocking settings.
> >
> > Are you able to reproduce the behavior on your Pi?
>
> I did not have any problems with USB recently (using 4.5),
> so I would not have any idea how to reproduce it.
>
> Note that I am using it with an AXIS USB-ethernet dongle plus USB-stick
> all the time on my Compute Module connected via a tiny hub,
> so I wonder if that qualifies as being able to trigger the issue...

the probe problem appears after applying John's patch series (it's not in 4.5):

[RFT PATCH 1/2] usb: dwc2: Add a 10 ms delay to dwc2_core_reset()
[RFT PATCH 2/2] Revert "usb: dwc2: Fix probe problem on bcm2835"

Please follow the complete discussion here [1].

[1] - http://marc.info/?l=linux-kernel&m=145711582915801&w=2

>
> Martin