Hello Linus,
Sorry for the noise, my mail was filtered by several ML because of some
HTML contents.
Le 26/11/2013 14:46, Linus Walleij a écrit :
On Thu, Nov 21, 2013 at 11:34 AM, boris brezillon
<b.brezillon@xxxxxxxxxxx> wrote:
On 21/11/2013 10:48, Linus Walleij wrote:
No matter whether it's a switch or a GPIO regulator it seems we
are in violent agreement that it should not be controlled by the
pin control states at least.
Start with making it a GPIO then you can figure out whether
a GPIO regulator or drivers/extcon/extcon-gpio.c should be
used.
Thanks for pointing this out. I wasn't aware of the extcon subsystem.
Actually, I think it's a little bit more tricky.
Hm, yeah extcon is for things like audio jacks on phones that
userspace need to detect.
drivers/input/keyboard/gpio_keys* is for things that actually
input characters to userspace stuff.
None of it is applicable here it seems ...
The switch connected to gpio PB22 is used to enable one device or the other:
- PB22 set to high level enables slot0 of mmc0 (connect mmc signals to the
mmc
connector)
- PB22 set to low level enables the dataflash (connect to the SPI0 signals
to the
dataflash device)
So this is something like a "jumper" of the old type, configuring
the entire system?
Something like that:
http://www.mignonette-game.com/images/v2/21-arduino-com-jumper.jpg
But in this case it is a mechanical switch rather than a jumper?
Not exactly.
The functionnaly selection (spi device or mmc slot) is done by the
software using to the
PB22 pin:
- set PB22 pin to 1 if you want to enable the mmc slot
- set PB22 pin to 0 if you want to enable the spi device
This is the rm9200ek board datasheet
http://www.alliedelec.com/images/products/datasheets/bm/ATMEL/70123901.pdf,
and you'll find the switch schematic at page 26.
Here is the switch datasheet :
http://pdf1.alldatasheet.fr/datasheet-pdf/view/90971/PERICOM/PI5A100Q.html
If I understand correctly, you're suggesting to retrieve the PB22 pin
value to decide
wether the mmc slot or the spi device is enabled. Is that right ?
In this case the bootstrap and/or bootloader would have to properly
configure the P22 pin
before executing the linux kernel, and I'm pretty sure this is not the case.
This is not much different from the GPIOs people use to e.g. encode
the board type, just that it can change.
Do people switch this thing at runtime?
In the board version this was configured in the init_machine function
(or board init
function) depending on the MTD_AT91_DATAFLASH_CARD
(
http://lxr.free-electrons.com/source/arch/arm/mach-at91/board-rm9200ek.c#L173).
As a result it was not reconfigurable at runtime.
But Jean-Christophe suggested to make it configurable at runtime (using
dt fragments).
The pinctrl approach has the benefit of providing a transparent way (no
existing
drivers modifications) to enable one device or the other.
But if you think this is better done (or cleaner) with an extcon or a
regulator device,
I'll try to find a way to do it this way.
I'm uncertain. If this is something that changes at runtime, the
input from the switch should be read through GPIO and used
to select the "default" state of one device and something like
"sleep" on the other (I suspect more things than pin control
may be affected by that!)
If this is a switch that you want to take the simple shortcut
of just reading at boot, the approach would still be similar, just
less code.
So use gpio_get() to read the value, and then select which
*entire device* goes active depending on the setting would
be the right approach I guess?
I'm not sure these suggestions apply according to my previous answers,
but tell me if I'm wrong.
Thanks for your time and suggestions.
Best Regards,
Boris
Yours,
Linus Walleij
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
