On Thu, Oct 6, 2016 at 11:55 AM, Jagan Teki jagannadh.teki@gmail.com wrote:
On Thu, Oct 6, 2016 at 9:21 PM, George McCollister george.mccollister@gmail.com wrote:
On Thu, Oct 6, 2016 at 10:27 AM, Jagan Teki jagannadh.teki@gmail.com wrote:
On Thu, Oct 6, 2016 at 8:32 PM, George McCollister george.mccollister@gmail.com wrote:
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().
Does stm_lock can't protect the Winbond? how different is in the process of doing when compared to stm?
stm_lock() does work with the Winbond parts. The issue is that you can simply unlock from software (stm_unlock). To make it impossible to write to the flash from software you must use stm_lock() then use the status register protect bits to prevent an unlock.
So, you need even if stm_unlock triggered from cmd flash still lock? then what is the point of using unlock?
stm_lock()/stm_unlock() change the block protect bits in the status register to lock/unlock flash blocks. The status register protect bits allow changes to the status register to be blocked under certain conditions (if /WP pin is low, until re-powered or permanently).
Just describe me what is the diff b/w winbond vs other stm flash in case of lock and unlocking.
I think it may be the same but if you have a part number this code is known to work with I'll get the datasheet and check. The comment above stm_lock() actually mentions a Winbond part! As far as I can tell STMicroelectronics no longer manufactures SPI Flash.
thanks!
Jagan Teki Free Software Engineer | www.openedev.com U-Boot, Linux | Upstream Maintainer Hyderabad, India.