macronix ONFI nand flash OTP support

[Miquel RAYNAL]

Hi Marek,

+CC: NAND maintainers Boris and Richard

> Hi,
> 
> I'm trying to add find out how to use OTP area in Macronix
> MX30LF4G18AC flash. AFAIU it is ONFI based flash and I did some quick
> hack and I can set/reset flash to go to OTP mode via get/set_features
> function available in nand_base.c.

Ok, so until now you can enter/leave OTP mode with get/set_features(),
right ?

> But for read page I need to send
> according datasheet:
> To use the PAGE READ command for reading data from the OTP area, issue
> the 00h command, and then issue five address cycles: for the first two
> cycles, the column address; and for the remaining address cycles,
> select a page in the range of 02h-00h-00h through 1Fh-00h-00h. Lastly,
> issue the 30h command. The PAGE READ CACHE MODE command is not
> supported on OTP pages.

This is the description of a normal READ operation, there is nothing
specific to OTP.

> 
> I did check nand_do_read_ops function but it's not sending e.g. 0x30
> which should be at the end of command. I'm using 4.1 kernel but
> checked also 4.14 and no such functionality is added even there.
> Nobody is using OTP area in nand flashes ;) ? Thanks for any pointers.

I suppose you added some tweaks to enable OTP and use nand_do_read_ops,
because there is currently no implementation for that in the NAND
framework (I think there is something in MTD layer though). But must
importantly, nand_do_read_ops basically calls chip->ecc.read*() which
is handled by the controller driver, so what driver are you using ?

How (where) did you trace the commands sent to the NAND chip ? For
instance, if you just looked at the arguments of ->cmdfunc(), it is
normal not to see any READSTART (0x30) command as it should be added
automatically later in the function. If the driver implements
->cmd_ctrl(), you may see there what exactly is sent to the device.

Thanks,
Miquèl