Messages in this thread | | | Date | Tue, 26 Nov 2013 18:55:52 +0100 | From | boris brezillon <> | Subject | Re: [PATCH 5/9] ARM: at91/dt: add mmc0 slot0 support to at91rm9200ek board |
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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@overkiz.com> 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
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