The issue is introduced in 571864e8ae. The
esp_flash API tries to clear the QE bit when the flash is not working in
quad modes.
However this introduces a regression, compared to earlier versions and
the legacy API. When the chip is not detected, the generic chip driver
is used, which cannot 100% handle the QE bit properly for all flash
vendors. There may be some flash chips (e.g. MXIC) that can be used in
dual modes by legacy API, but output wrong data when the esp_flash API
clears the QE bit in a wrong way.
This commit reverts the QE force clearing behavior, so that it's safer
for the generic chip driver to work under dual modes.
The default chip driver (chip_generic) use command 01H + 2 bytes to
clear the QE bit. However this will accidently change the configuration
register value of the MXIC chip.
MXIC chip driver is added to fix that.
Cao Sen Miao