Hello,
On 19/12/2013 19:22, Felipe Balbi wrote:
On Thu, Dec 19, 2013 at 06:18:40PM +0100, boris brezillon wrote:
Hello Felipe,
On 19/12/2013 17:47, Felipe Balbi wrote:
On Thu, Dec 19, 2013 at 08:41:09AM -0800, Greg Kroah-Hartman wrote:
On Thu, Dec 19, 2013 at 03:34:31PM +0100, Boris BREZILLON wrote:
GPIO hogging is a way to request and configure specific GPIO without
explicitly requesting it in the device driver.
The request and configuration procedure is handled in the core device
driver code before the driver probe function is called.
It allows specific GPIOs to be configured without any driver specific code.
Particularly usefull when a external device is connected to a bus and the
bus connections depends on an external switch controlled by a GPIO pin.
for external switches, you probably need a pinctrl-gpio driver.
Do you mean using pinctrl pinconf to configure the PIN as output-high or
output-low ?
This was my first proposal
(see https://www.mail-archive.com/devicetree@xxxxxxxxxxxxxxx/msg05829.html).
My mistake: this is not exactly what I proposed in my patch series.
Actually, I was directly requesting the pin connected to the external
switch as
OUTPUT + (OUTPUT-LEVEL) according the the device needs:
- output high for MMC slot
- output low for SPI device
And, I guess this is why Linus asked me to find a better solution.
IMHO your approach is, by far, much better. You expose the external switch
as a PIN muxing device and the devices connected to through this PIN mux
block just have to request the appropriate PIN states.
In my specific case this would give the following:
- MMC conf for mmc slot 0
- SPI conf for the SPI device
With your approach the HW representation is better: the different signals
controlled by the external switch can be seen using debugfs, and device
tree definition is closer to the real HW design.
that's quite a weird argument from Linus W, considering you _do_ have a
discrete mux on the board.
We have quite a few of such "crazy" scenarios here at TI and we were
going to send a pinctrl-gpio driver. If that's not acceptable, then I
suppose there is no way to boot from NAND on a board where NAND signals
go through a discrete mux where the select signal is a GPIO pin.
Please keep going with the submission process: I'm really interested in this
driver (BTW could you add me in the CC list ?).
Linus, tell me if I'm wrong, but I think, the pinctrl-gpio is the right
way to solve
the at91rm9200ek board use case.
This does not mean, the gpio hogs approach does not solve other issues (see
https://lkml.org/lkml/2013/8/29/333 and
https://www.mail-archive.com/linux-gpio@xxxxxxxxxxxxxxx/msg01084.html),
but in
my specific case, I'd rather use the pinctrl-gpio driver.
Best Regards,
Boris
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