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From: Rob Herring <robh@kernel.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Matthias Kaehlcke <mka@chromium.org>,
	Doug Anderson <dianders@chromium.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Frank Rowand <frowand.list@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux USB List <linux-usb@vger.kernel.org>,
	Bastien Nocera <hadess@hadess.net>,
	Stephen Boyd <swboyd@chromium.org>,
	Ravi Chandra Sadineni <ravisadineni@chromium.org>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>, Peter Chen <peter.chen@nxp.com>
Subject: Re: [PATCH v4 1/2] dt-bindings: usb: Add binding for discrete onboard USB hubs
Date: Mon, 5 Oct 2020 14:59:04 -0500	[thread overview]
Message-ID: <CAL_JsqK8V9PUCUD1iZQr52b28G39JraY=doZWzk0gNvu15qW-g@mail.gmail.com> (raw)
In-Reply-To: <20201005193611.GA389867@rowland.harvard.edu>

On Mon, Oct 5, 2020 at 2:36 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Mon, Oct 05, 2020 at 12:18:12PM -0700, Matthias Kaehlcke wrote:
> > On Mon, Oct 05, 2020 at 12:15:27PM -0400, Alan Stern wrote:
> > > The conclusion is that we need to have code that is aware of some
> > > detailed needs of a specific device but is not part of the device's
> > > driver.  I'm not sure what the best way to implement this would be.
> >
> > Wouldn't it be possible to load the module when the DT specifies that
> > the device exists? For USB the kernel would need the VID/PID to identify
> > the module, these could be extracted from the compatible string.
>
> Loading a driver module whenever DT says a device exists?  Not a bad
> idea.  I don't know what would be involved, but no doubt it is possible.

MODULE_DEVICE_TABLE mostly as I mentioned in my other reply.

> Note that, except for a few special cases, the kernel identifies the
> appropriate driver for USB hubs not by the VID/PID but instead by the
> device class or interface class.  I suppose the compatible string could
> include that information too?

We can go back to 1998 OpenFirmware and it's already there[1].
'usb,class9' for a hub. There's a few other variations defined.

> > Having the initialization code outside of the driver could lead to code
> > duplication, since the driver might want to power the device down in
> > certain situations (e.g. system suspend).
>
> True.  On the other hand, how common do you think it would be for
> drivers not to want to mess with the power settings?

I think in that case you'd generally want firmware to enable things
and the kernel then does no power control.

We have ~1500 boards using DT and maybe ~10 with USB devices described
in DT. So the whole thing is not common to begin with.

Rob

[1] https://www.devicetree.org/open-firmware/bindings/usb/usb-1_0.ps

  reply	other threads:[~2020-10-05 19:59 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-28 17:13 [PATCH v4 1/2] dt-bindings: usb: Add binding for discrete onboard USB hubs Matthias Kaehlcke
2020-09-28 17:13 ` [PATCH v4 2/2] USB: misc: Add onboard_usb_hub driver Matthias Kaehlcke
2020-09-28 18:47   ` Alan Stern
2020-09-29  1:43     ` Matthias Kaehlcke
2020-09-29 16:00       ` Alan Stern
2020-09-29 16:50         ` Matthias Kaehlcke
2020-09-28 22:03   ` Doug Anderson
2020-09-29  1:59     ` Matthias Kaehlcke
2020-09-28 22:13 ` [PATCH v4 1/2] dt-bindings: usb: Add binding for discrete onboard USB hubs Doug Anderson
2020-09-29  2:14   ` Matthias Kaehlcke
2020-09-29 20:17 ` Rob Herring
2020-09-29 22:09   ` Matthias Kaehlcke
2020-09-30  1:32     ` Alan Stern
2020-09-30 12:49       ` Matthias Kaehlcke
2020-09-30 14:44         ` Rob Herring
2020-09-30 15:28           ` Doug Anderson
2020-09-30 18:00             ` Doug Anderson
2020-09-30 19:19               ` Rob Herring
2020-10-01 21:39                 ` Matthias Kaehlcke
2020-09-30 19:19             ` Alan Stern
2020-09-30 20:20             ` Rob Herring
2020-10-01  1:24               ` Alan Stern
2020-10-01 21:54                 ` Matthias Kaehlcke
2020-10-02  1:21                   ` Alan Stern
2020-10-02 16:08                     ` Matthias Kaehlcke
2020-10-02 18:48                       ` Alan Stern
2020-10-02 17:08               ` Doug Anderson
2020-10-02 18:36                 ` Alan Stern
2020-10-02 22:58                   ` Rob Herring
2020-10-03 12:41                     ` Alan Stern
2020-10-05 16:06                       ` Matthias Kaehlcke
2020-10-05 16:15                         ` Alan Stern
2020-10-05 19:18                           ` Matthias Kaehlcke
2020-10-05 19:36                             ` Alan Stern
2020-10-05 19:59                               ` Rob Herring [this message]
2020-10-05 23:29                                 ` Matthias Kaehlcke
2020-10-05 19:36                             ` Rob Herring
2020-10-05 19:20                         ` Rob Herring
2020-10-02 22:28                 ` Rob Herring
2020-10-02 23:09                   ` Doug Anderson
2020-10-06  0:45                     ` Matthias Kaehlcke
2020-10-06 14:18                       ` Alan Stern
2020-10-06 16:59                         ` Matthias Kaehlcke
2020-10-06 17:15                           ` Alan Stern
2020-10-06 19:25                             ` Matthias Kaehlcke
2020-10-07  1:00                               ` Alan Stern
2020-10-07 16:03                                 ` Matthias Kaehlcke
2020-10-07 16:38                                   ` Alan Stern
2020-10-07 17:28                                     ` Matthias Kaehlcke
2020-10-07 19:25                                       ` Alan Stern
2020-10-07 19:42                                         ` Matthias Kaehlcke
2020-10-07 20:17                                           ` Alan Stern
2020-10-07 21:42                                             ` Matthias Kaehlcke
2020-10-08 14:09                                               ` Alan Stern
2020-10-09 23:13                                                 ` Matthias Kaehlcke

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