Re: Implementing bus recovery

[Simon Lindgren <simon-IfRblWqrl23QT0dZR+AlfA@public.gmane.org>]

Den 2014-08-23 02:41, Mark Roszko skrev:
> Prepare_recovery and unprepare_recovery are to configure the pad
> multiplexer since thats platform specific. You don't care about the
> adapter reference as you just need the scl_gpio and sda_gpio values to
> know what pins to reconfigure.
>
> In fact Atmel's pad mux functions look like this:
>
> at91_set_A_periph(unsigned pin, int use_pullup)
> at91_set_B_periph(unsigned pin, int use_pullup)
> at91_set_C_periph(unsigned pin, int use_pullup)
> .....
>
>
> Here's the latest(or close) driver specific patch that slipped through
> the cracks it seems?
> http://www.spinics.net/lists/linux-i2c/msg11357.html
>

We are using a sama5d3-based machine which is almost entirely dt based, 
so passing callbacks to the driver using the platform data seems like a 
bad fit. Hard coding these calls in the driver won't really work either 
(even for a single machine) since not all instances of the adapter exist 
on the same peripheral. Ie, one adapter is on peripheral A and the 
others are on peripheral B for this specific soc.

The way I assumed it would work was to declare a "recovery" pinmux state 
in the device tree and then switch to that during the recovery and then 
back to default once it's done. Could you expand a bit on this please?

>
> Bus_recovery itself you have to call in the at91 driver on a
> controller timeout just like the patch does.
>   if (ret == 0) {
>                   dev_err(dev->dev, "controller timed out\n");
> -                at91_init_twi_bus(dev);
>   +                if (i2c_recover_bus(dev->adapter->bus_recovery_info) < 0)
>   +                      at91_init_twi_bus(dev);
>
>                   ret = -ETIMEDOUT;
>                   goto error;
> }
>
> the call stack looks something like this
>
> --at91_twi_xfer
> ----- i2c_recover_bus
> --------- i2c_generic_gpio_recovery
> -------------i2c_get_gpios_for_recovery  (requests gpios)
> -------------i2c_generic_recovery
> ----------------prepare_recovery         (configure padmux to put gpio
> on the pin)
> ----------------get_sda, get_scl          (get gpio value, generic
> function by default is fine for atmel)
> ----------------set_scl                       (set scl value, generic
> function by default is fine for atmel)
> ----------------unrepare_recovery       (configure padmux to put twi
> back on the pin)
> -------------i2c_put_gpios_for_recovery (frees gpios)
>
>
> Somewhere in at91_twi_probe before the adapter is registered you also
> have to setup the bus_recovery_info struct and set recover_bus to the
> i2c_generic_gpio_recovery function similar to the patch linked.
>

That matches my previous understanding, thanks for the confirmation.