cfi_cmdset_0002: reading and writing one time programmable memory

[Christian Riesch <christian.riesch@omicron.at>]

Hello,

I would like to extend the AMD command set for reading/writing/locking 
of one time programmable (OTP) memory areas (called secure silicon in 
Spansion device, called extended memory region in Micron devices...). In 
particular I would like to support the 256 byte extended memory region 
of Micron M29EW devices. Currently the code in 
drivers/mtd/chips/cfi_cmdset_0002.c only supports reading of the first 8 
bytes of this memory area.

I have already implemented this support partially, but before posting a 
first patchset, I have a few questions regarding the current code in 
do_read_secsi_onechip() in drivers/mtd/chips/cfi_cmdset_0002.c.

This function first waits for the chip to get into FL_READY state? Could 
the get_chip() function be used instead here?

After sending the 0xaa/0x55/0x88 command to the device, the 
OTP/SecSi/... memory is mapped to addresses 0x00 - 0xff of the device. 
Does this require putting xip_disable/xip_enable around this code? 
Should the cache get invalidated before reading? Should the function get 
marked __xipram?

Thanks for your help!
Christian