NXP drivers: flash: soc_flash_mcux: remove CMD_MARGIN_CHECK

[DerekSnell]

The CMD_BLANK_CHECK can return errors when the flash is readable, and should only be used after programming, not in is_area_readable(). From the LPC55S69 datasheet: "As cells age and lose charge, a correctly programmed address will fail this check, while still being able to be read successfully for the remaining duration of the data retention time."

Resolves #83599

[phonkane]

A bit late with my comment but I wonder if this works as intended. According to LPC55 User Manual, "If a page is found which is not correctly erased, the FAIL flag is set". I get it that if the FAIL flag is not set (i.e. page is not blank), reading this page is safe. However shouldn't the test be repeated for each page in the range passed to is_area_readable()? It looks like the FAIL flag is set if any of the pages in the range is programmed, but this does not mean it is safe to read the entire range. Admittedly this should work just fine as long as the same flash region is always completely programmed or erased.

Also the commit message is a bit confusing, I guess "CMD_BLANK_CHECK can return errors" should be read as "CMD_MARGIN_CHECK can return errors"?

[DerekSnell]

Hi @phonkane ,
Great point, and thank you for raising this up. We agree with your concern, and I created this issue #86432 to track updating that driver.

And yes, I had an error in the commit message. It should read "The CMD_MARGIN_CHECK can return errors when the flash is readable...". Sorry I cannot update that commit message now.

Thank you for raising this.