From: Alan Stern <stern@rowland.harvard.edu>
To: Doug Anderson <dianders@chromium.org>
Cc: "Felipe Balbi" <balbi@ti.com>,
"John Youn" <John.Youn@synopsys.com>,
"Yunzhi Li" <lyz@rock-chips.com>,
"Heiko Stübner" <heiko@sntech.de>,
"open list:ARM/Rockchip SoC..."
<linux-rockchip@lists.infradead.org>,
"Julius Werner" <jwerner@chromium.org>,
"Herrero, Gregory" <gregory.herrero@intel.com>,
"Kaukab, Yousaf" <yousaf.kaukab@intel.com>,
"Dinh Nguyen" <dinguyen@opensource.altera.com>,
"John Youn" <johnyoun@synopsys.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/2] usb: dwc2: host: Fix missing device insertions
Date: Mon, 16 Nov 2015 15:31:55 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1511161523290.1938-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <CAD=FV=VmV8K=ytmy_1fviG-9mxyT3aoSyX7nOg2KKXT_05h_TA@mail.gmail.com>
On Mon, 16 Nov 2015, Doug Anderson wrote:
> Alan,
>
> On Mon, Nov 16, 2015 at 11:31 AM, Alan Stern <stern@rowland.harvard.edu> wrote:
> > On Mon, 16 Nov 2015, Doug Anderson wrote:
> >
> >> ---
> >>
> >> usb: dwc2: host: Fix missing device insertions
> >>
> >> If you've got your interrupt signals bouncing a bit as you insert your
> >> USB device, you might end up in a state when the device is connected but
> >> the driver doesn't know it.
> >>
> >> Specifically, the observed order is:
> >> 1. hardware sees connect
> >> 2. hardware sees disconnect
> >> 3. hardware sees connect
> >> 4. dwc2_port_intr() - clears connect interrupt
> >> 5. dwc2_handle_common_intr() - calls dwc2_hcd_disconnect()
> >>
> >> Now you'll be stuck with the cable plugged in and no further interrupts
> >> coming in but the driver will think we're disconnected.
> >>
> >> We'll fix this by checking for the missing connect interrupt and
> >> re-connecting after the disconnect is posted. We don't skip the
> >> disconnect because if there is a transitory disconnect we really want to
> >> de-enumerate and re-enumerate.
> >
> > Why do you need to do anything special here? Normally a driver's
> > interrupt handler should query the hardware status after clearing the
> > interrupt source. That way no transitions ever get missed.
> >
> > In your example, at step 5 the dwc2 driver would check the port status
> > and see that it currently is connected. Therefore the driver would
> > pass a "connect status changed" event to the USB core and set the port
> > status to "connected". No extra checking is needed, and transitory
> > connects or disconnects get handled correctly.
>
> Things are pretty ugly at the moment because the dwc2 interrupt
> handler is split in two. There's dwc2_handle_hcd_intr() and
> dwc2_handle_common_intr(). Both are registered for the same "shared"
> IRQ. If I had to guess, I'd say that this is probably because someone
> wanted to assign the ".irq" field in the "struct hc_driver" for the
> host controller but that they also needed the other interrupt handler
> to handle things shared between host and gadget mode.
>
> In any case, one of these two interrupt routines handles connect and
> the other disconnect. That's pretty ugly but means that you can't
> just rely on standard techniques for keeping things in sync.
Okay, that is rather weird. Still, I don't see why it should matter.
Fundamentally there's no difference between a "connect" interrupt and a
"disconnect" interrupt. They should both do exactly the same things:
clear the interrupt source, post a "connection change" event, and set
the driver's connect status based on the hardware's current state.
The second and third parts can be handled by a shared subroutine.
If you think of these things as "connect changed" interrupts rather
than as "connect" and "disconnect" interrupts, it makes a lot of sense.
> It would probably be a pretty reasonable idea to try to clean that up
> more, but that would be a very major and intrusive change.
Maybe so -- I'll take your word for it since I'm not at all familiar
with the dwc2 code.
Alan Stern
next prev parent reply other threads:[~2015-11-16 20:31 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-03 20:30 [PATCH v2 1/2] usb: dwc2: host: Fix missing device insertions Douglas Anderson
2015-11-03 20:30 ` [PATCH v2 2/2] usb: dwc2: host: Clear interrupts before handling them Douglas Anderson
2015-11-05 3:08 ` John Youn
2015-11-16 16:28 ` Felipe Balbi
2015-11-16 17:22 ` Doug Anderson
2015-11-19 1:43 ` John Youn
2015-11-19 16:37 ` Doug Anderson
2015-11-19 18:19 ` Felipe Balbi
2015-11-19 19:09 ` John Youn
2015-11-05 2:52 ` [PATCH v2 1/2] usb: dwc2: host: Fix missing device insertions John Youn
2015-11-16 17:44 ` Felipe Balbi
2015-11-16 18:13 ` Doug Anderson
2015-11-16 18:22 ` Felipe Balbi
2015-11-16 18:44 ` Doug Anderson
2015-11-16 19:09 ` Felipe Balbi
2015-11-16 19:31 ` Alan Stern
2015-11-16 19:46 ` Doug Anderson
2015-11-16 20:26 ` Julius Werner
2015-11-16 20:38 ` Alan Stern
2015-11-16 20:31 ` Alan Stern [this message]
2015-11-16 23:14 ` Doug Anderson
2015-11-17 1:53 ` John Youn
2015-11-17 2:37 ` Doug Anderson
2015-11-17 15:40 ` Alan Stern
2015-11-17 16:13 ` Doug Anderson
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