linux-kernel - Re: [PATCH v2 1/2] usb: dwc2: host: Fix missing device insertions

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Date:	Tue, 17 Nov 2015 10:40:37 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Doug Anderson <dianders@...omium.org>
cc:	Felipe Balbi <balbi@...com>, John Youn <John.Youn@...opsys.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 v2 1/2] usb: dwc2: host: Fix missing device insertions

On Mon, 16 Nov 2015, Doug Anderson wrote:

> > 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.
> 
> Ah, sorry I misunderstood.  OK, fair enough.  So you're saying that
> the problem is that dwc2_hcd_disconnect() has a line that looks like
> this:
> 
>   hsotg->flags.b.port_connect_status = 0;
> 
> ...and the dwc2_port_intr() has a line that looks like this:
> 
>   hsotg->flags.b.port_connect_status = 1;
> 
> ...and both should just query the status.

Well, I don't know how the driver uses flags.b.port_connect_status.  In 
principle it could do away with that flag completely and always query 
the hardware status.

> Do you think we should to block landing this patch on cleaning up how
> dwc2 handles port_connect_status?  I'm not sure what side effects
> changing port_connect_status will have, so I'll need to test and dig a
> bit...
> 
> I'm currently working on trying to fix the microframe scheduler and
> was planning to post the next series of patches there pretty soon.
> I'm also planning to keep digging to figure out how to overall
> increase compatibility with devices (and compatibility with many
> devices plugged in).
> 
> If it were up to me, I'd prefer to land this patch in either 4.4 or
> 4.5 since it does seem to work.  ...then put seeing what we can do to
> cleanup all of the port_connect_status on the todo list.

It's up to you guys.  All I've been doing here is pointing out that
your proposed approach didn't seem like the best.

Alan Stern

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