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

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Message-ID: <20150108082510.GA19346@kuha.fi.intel.com>
Date:	Thu, 8 Jan 2015 10:25:10 +0200
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	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 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.

-- 
heikki
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