linux-kernel - Re: [RFC PATCH] gpio: support for GPIO forwarding

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Message-ID: <1445095.bPkYZhscYx@vostro.rjw.lan>
Date:	Thu, 15 Jan 2015 10:21:24 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] gpio: support for GPIO forwarding

On Thursday, January 08, 2015 10:25:10 AM Heikki Krogerus wrote:
> On Thu, Dec 18, 2014 at 10:23:18AM +0200, Heikki Krogerus wrote:
> > This makes it possible to assign GPIOs at runtime. The
> > motivation for it is because of need to forward GPIOs from
> > one device to an other. That feature may be useful for
> > example with some mfd devices, but initially it is needed
> > because on some Intel Braswell based ACPI platforms the GPIO
> > resources controlling signals of the USB PHY are given to
> > the controller device object for whatever reason, so the
> > driver of that controller needs be able to pass them to the
> > PHY device somehow.
> > 
> > So basically this is meant to allow patching of bad (bad
> > from Linux kernels point of view) hardware descriptions
> > provided by system fw in the drivers.
> > 
> > Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > ---
> > 
> > Hi,
> > 
> > I'm sending this first as a RFC in case you guys have some better
> > idea how to solve our problem. I actually already have couple
> > platforms where the GPIO resources are given to the "wrong" device
> > objects now.
> > 
> > Originally we were thinking about simply handling our problem with
> > hacks to the PHY drivers, basically also checking if the parent has
> > GPIOs. That would only work if the controller is always the parent,
> > which it's not, but even if it was, it would be too risky. The PHY
> > drivers don't know which controller they are attached to, so what is
> > to say that the GPIOs aren't really attached to the controller.
> > 
> > So the safest way to handle our problem is to deal with it in quirks
> > in the controller drivers. Solving it by bouncing the GPIOs did not
> > feel ideal there doesn't seem to be any other way. The API is copied
> > from clkdev (clk_register_clkdev). In the end it's really only one
> > function for adding the lookups and one for removing them.
> > 
> > The way it's implemented is by modifying the current style of handling
> > the lookups a little bit. The per device lookup table is basically
> > reverted back to the single linked-list format since it seems that
> > these lookups may have to be assigned from several sources.
> > 
> > Thanks,
> 
> Gentle ping on this.

Please CC patches involving ACPI in *any* *way* way to linux-acpi@...r.kernel.org.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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