linux-kernel - Re: [PATCH 0/4] usb: Use notifier for linking Type C ports.

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Date:   Tue, 30 Nov 2021 13:03:43 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Prashant Malani <pmalani@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        wonchung@...gle.com, bleung@...omium.org,
        Alan Stern <stern@...land.harvard.edu>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        Rajat Jain <rajatja@...gle.com>,
        Rikard Falkeborn <rikard.falkeborn@...il.com>,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH 0/4] usb: Use notifier for linking Type C ports.

Hi Prashant,

On Fri, Nov 26, 2021 at 11:40:49AM +0200, Heikki Krogerus wrote:
> On Wed, Nov 24, 2021 at 03:10:06PM -0800, Prashant Malani wrote:
> > This series resolves the cyclic dependency error which was introduced by
> > commit 63cd78617350 ("usb: Link the ports to the connectors they are
> > attached to") which lead to it being reverted. The approach here is to
> > use a notifier to link a new Type C port to pre-existing USB ports
> > instead of calling an iterator of usb ports from the Type C connector
> > class. This allows commit 63cd78617350 ("usb: Link the ports to the
> > connectors they are attached to") to then be submitted without any
> > depmod cyclic dependency error.
> > 
> > The final patch removes the usb port iterator since it is no longer
> > needed.
> 
> This is not enough. Build the Type-C Class as a module and the USB bus
> statically, and the links will not get created.
> 
> I'm not sure you actually achieve much with this series, and I'm not
> sure this approach will ever fully solve the problem. As long as we
> have to declare API, we will have the circular dependency issue on our
> hands. But there are ways to avoid that.
> 
> There is for example the component framework (drivers/base/component.c)
> that I've been thinking about using here. In this case it would work
> so that you declare the USB Type-C part as your aggregate driver, and
> everything that is connected to it (so USB ports, DisplayPorts, TBT,
> etc.) would then just declare themselves as general components. Could
> you take a look at that?

I'm preparing a patch where I store all _PLDs in the ACPI tables, and
create list of devices that share it. I can convert port-mapper.c to
it and the component framework while at it.


Br,

-- 
heikki