Re: [PATCH v4 2/2] usb: dwc2: host: Clear interrupts before handling them

From: Doug Anderson <dianders@chromium.org>
To: Felipe Balbi <balbi@ti.com>
Cc: "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 v4 2/2] usb: dwc2: host: Clear interrupts before handling them
Date: Fri, 20 Nov 2015 09:04:48 -0800	[thread overview]
Message-ID: <CAD=FV=X6N=_=B2pLTFwK2OP-pqoR_3B3+gynJQaCCOh4DsUPJg@mail.gmail.com> (raw)
In-Reply-To: <CAD=FV=XBOmi_oH1jTnLABzVEssTeyVDQm9ocbfuO+gGjAFOCtg@mail.gmail.com>

Hi,

On Fri, Nov 20, 2015 at 8:49 AM, Doug Anderson <dianders@chromium.org> wrote:
> Felipe,
>
> On Fri, Nov 20, 2015 at 7:40 AM, Felipe Balbi <balbi@ti.com> wrote:
>>
>> Hi,
>>
>> Douglas Anderson <dianders@chromium.org> writes:
>>> In general it is wise to clear interrupts before processing them.  If
>>> you don't do that, you can get:
>>>  1. Interrupt happens
>>>  2. You look at system state and process interrupt
>>>  3. A new interrupt happens
>>>  4. You clear interrupt without processing it.
>>>
>>> This patch was actually a first attempt to fix missing device insertions
>>> as described in (usb: dwc2: host: Fix missing device insertions) and it
>>> did solve some of the signal bouncing problems but not all of
>>> them (which is why I submitted the other patch).  Specifically, this
>>> patch itself would sometimes change:
>>>  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()
>>>
>>> ...to:
>>>  1. hardware sees connect
>>>  2. hardware sees disconnect
>>>  3. dwc2_port_intr() - clears connect interrupt
>>>  4. hardware sees connect
>>>  5. dwc2_handle_common_intr() - calls dwc2_hcd_disconnect()
>>>
>>> ...but with different timing then sometimes we'd still miss cable
>>> insertions.
>>>
>>> In any case, though this patch doesn't fix any (known) problems, it
>>> still seems wise as a general policy to clear interrupt before handling
>>> them.
>>>
>>> Note that for dwc2_handle_usb_port_intr(), instead of moving the clear
>>> of PRTINT to the beginning of the function we remove it completely.  The
>>> only way to clear PRTINT is to clear the sources that set it in the
>>> first place.
>>>
>>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
>>> Acked-by: John Youn <johnyoun@synopsys.com>
>>> Tested-by: John Youn <johnyoun@synopsys.com>
>>
>> $ patch -p1 --dry-run < patch.diff
>> checking file drivers/usb/dwc2/core_intr.c
>> checking file drivers/usb/dwc2/hcd_intr.c
>> Hunk #4 FAILED at 365.
>> Hunk #5 succeeded at 388 (offset 11 lines).
>> 1 out of 5 hunks FAILED
>>
>> Care to rebase on top of my testing/next ?
>
> No problem.
>
> ...though when I did that, I actually found (by code inspection) a bug
> in the original patch, so I guess it's a good thing it didn't apply...
> ...and then that led me to another bug that was pre-existing.  I'll
> send up two new patches shortly.  I'll remove John's Ack and Tested
> tags from the patch since it contains a change.
>
> It looks like you already landed part 1 of this series (usb: dwc2:
> host: Fix missing device insertions) so I won't resend that.

Ah, OK.  Now I see why nobody found these problems in testing.  The
code path is completely disabled by all current parameters as checked
in to mainline.  In any case, it's good to fix.

-Doug