[linux-sunxi] Re: [RFC PATCH v2 09/14] mtd: nand: add sunxi NFC dt bindings doc

[boris brezillon dev]

Hello Henrik,

On 29/01/2014 23:37, Henrik Nordström wrote:
> ons 2014-01-29 klockan 11:11 -0600 skrev Rob Herring:
>
>> Isn't allwinner,rb implied by a lack of rb-gpios property. Or no R/B
>> pin is an option? If so, don't you need some fixed time delay
>> properties like max erase time?
>>
>> rb-gpios could be added to the generic nand binding as well.
> The Allwinner NAND controller have dedicated RB pins when NAND is
> enabled, only MUXed with other functions when NAND is not enabled.
>
> Leaving RB unconnected is not a valid hardware configuration. The
> controller internal timing engine depends on being able to sense RB to
> sequence NAND commands properly.

This is not true (at least in this driver). It was in yuq's driver because
he was using the NFC_WAIT_FLAG ,and in this case the controller wait
for the native R/B pin to be high before considering the CMD is complete.

This driver choose the appropriate way to test the R/B state of the
NAND chip according to what was specified in the DT:
- allwinner,rb: native R/B id. These pins will be used by the NAND
   controller to test the R/B state. Only 0 and 1 are valid because the
   NAND controller only support 2 R/B pins.
- rb-gpios: gpio used for R/B tests. This is a simple GPIO and will
   use the GPIO subsystem to test the R/B pin state.
- none: the NAND base code will wait some time before and send
   STATUS cmd to the NAND to check its status.

BTW, the controller supports 8 CS (8 NAND chips), but only have 2 native
R/B pins, this means you'll have to use the GPIO or standard GET_STATUS
method if you connect 3 or more NAND chips.

And for the record, I still think the rb-gpios property (or whatever
common name you choose: nand-rb-gpios ?) should be part of
the generic NAND binding, because other controllers (at least the
atmel one :)) use GPIOs to test R/B state.

Best Regards,

Boris

>
> Regards
> Henrik
>