linux-kernel - Re: [PATCH v3 2/2] usb: dwc2: host: Clear interrupts before handling them

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Message-ID: <CAD=FV=V9AfWoeph34i2z37Ze93EYRA8NjwfX=CGhmOb6ufXRMQ@mail.gmail.com>
Date:	Thu, 19 Nov 2015 13:12:33 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Antti Seppälä <a.seppala@...il.com>
Cc:	John Youn <John.Youn@...opsys.com>, Felipe Balbi <balbi@...com>,
	Yunzhi Li <lyz@...k-chips.com>,
	Heiko Stübner <heiko@...ech.de>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Julius Werner <jwerner@...omium.org>,
	"Herrero, Gregory" <gregory.herrero@...el.com>,
	"Kaukab, Yousaf" <yousaf.kaukab@...el.com>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	John Youn <johnyoun@...opsys.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] usb: dwc2: host: Clear interrupts before handling them

Antti,

On Thu, Nov 19, 2015 at 1:09 PM, Antti Seppälä <a.seppala@...il.com> wrote:
> On 19 November 2015 at 21:45, Douglas Anderson <dianders@...omium.org> wrote:
>> 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.
>>
>> Signed-off-by: Douglas Anderson <dianders@...omium.org>
>> Acked-by: John Youn <johnyoun@...opsys.com>
>> Tested-by: John Youn <johnyoun@...opsys.com>
>> ---
>> Changes in v3:
>> - Don't (uselessly) clear the PRTINT anymore (Felipe Balbi).
>>
>> Changes in v2: None
>>
>
> Hi.
>
> It seems that towards the end of hcd_intr.c you seem to be switching a
> few calls of dwc2_writel() to plain writel(). It looks like something
> that is easily overlooked but please always use dwc2_writel to
> preserve correct register endianness on big-endian platforms.

Oops!  That was a very dumb oversight, thanks for catching.  Sorry
about that.  Fix coming.

-Doug
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