From: Matthias Kaehlcke <mka@chromium.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Rob Herring <robh@kernel.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 09:06:55 -0700 [thread overview]
Message-ID: <20201005160655.GA4135817@google.com> (raw)
In-Reply-To: <20201003124142.GA318272@rowland.harvard.edu>
On Sat, Oct 03, 2020 at 08:41:42AM -0400, Alan Stern wrote:
> On Fri, Oct 02, 2020 at 05:58:22PM -0500, Rob Herring wrote:
> > On Fri, Oct 2, 2020 at 1:36 PM Alan Stern <stern@rowland.harvard.edu> wrote:
> > > Regardless of how the situation is represented in DT, there remains the
> > > issue of where (i.e., in which driver module) the appropriate code
> > > belongs. This goes far beyond USB. In general, what happens when one
> > > sort of device normally isn't hooked up through a power regulator, so
> > > its driver doesn't have any code to enable a regulator, but then some
> > > system does exactly that?
> > >
> > > Even worse, what if the device is on a discoverable bus, so the driver
> > > doesn't get invoked at all until the device is discovered, but on the
> > > new system it can't be discovered until the regulator is enabled?
> >
> > Yep, it's the same issue here with USB, MDIO which just came up a few
> > weeks ago, MMC/SD which hacked around it with 'mmc-pwrseq' binding
> > (not something I want to duplicate) and every other discoverable bus.
> > What do they all have in common? The kernel's driver model being
> > unable to cope with this situation. We really need a common solution
> > here and not bus or device specific hack-arounds.
>
> To me this doesn't seem quite so much to be a weakness of the kernel's
> driver model.
>
> It's a platform-specific property, one that is not discoverable and
> therefore needs to be represented somehow in DT or ACPI or something
> similar. Something that says "Device A cannot operate or be discovered
> until power regulator B is enabled", for example.
>
> The decision to enable the power regulator at system startup would be
> kernel policy, not a part of the DT description. But there ought to be
> a standard way of recognizing which resource requirements of this sort
> should be handled at startup. Then there could be a special module (in
> the driver model core? -- that doesn't really seem appropriate) which
> would search through the whole DT database for resources of this kind
> and enable them.
This might work for some cases that only have a single resource or multiple
resources but no timing/sequencing requirements. For the more complex cases
it would probably end up in something similar to the pwrseq series
(https://lore.kernel.org/patchwork/project/lkml/list/?series=314989&state=%2A&archive=both),
which was nack-ed by Rafael, Rob also expressed he didn't want to go
down that road.
It seems to me that initialization of the resources needs to be done by
the/a driver for the device, which knows about the sequencing requirements.
Potentially this could be done in a pre-probe function that you brought up
earlier.
next prev parent reply other threads:[~2020-10-05 16:06 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 [this message]
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
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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