[U-Boot] sf: proposed status register protect

[George McCollister]

I'm looking into adding a sub-command to sf to protect status
registers on Winbond SPI flash parts via the status register protect
bits SRP0, SRP1. I propose the sub-command be named sr-protect.

My use case is simple, I want to make the SPI flash read-only when the
/WP pin is low. To do this I must do 'sf protect lock 0 $size' then
set SRP0 to 1 and hold the /WP pin low. Although my use case doesn't
require it, setting SRP1 to 1 allows either Power Supply Lock-Down or
One Time Program (if supported by hardware) and I would probably add
support for these as well.

All of the current Winbond SPI NOR flash part datasheets that I've
looked at show that the parts support the same locking implemented in
stm_lock() even though SPI_FLASH_CFI_MFR_WINBOND is not in the list of
vendors which use the function. I'll change this to make
SPI_FLASH_CFI_MFR_WINBOND parts use stm_lock(), stm_unlock(),
stm_is_locked().

spi_flash_protect() (which ultimately calls either stm_lock() or
stm_unlock()) is not part of the driver model (dm_spi_flash_ops).
Is there any issue with adding another function (let's call it
spi_flash_sr_protect) that is not part of the driver model?

Is anyone aware of any vendors other than Winbond that use this SRP
mechanism or should only SPI_FLASH_CFI_MFR_WINBOND parts use it?
For details see "7.1.7 Status Register Protect Bit (SRP1, SRP0)" on
page 15 of http://www.winbond.com/resource-files/w25q64cv_revh_052214[2].pdf

Cheers,
George McCollister