We have a board that feature NOR flash and hardware write protection is handled by controlling the write enable pin. When write protection is enabled, the nWE pin is forced high by external logic. The memory controller and/or CFI logic is unaware of this, and since CFI uses write enable as part of the CFI command set, a CFI probing will fail when write protection is enabled.
The rationale for controlling nWE and not WP (write protection) is that WP only protects the first sector of the device. In our case this is less than the size of the bootloader (U-boot), since that occupies two sectors. Due to this the built-in NOR write protection is rather useless.
Our current solution based on controlling nWE is to hardcode flash geometry in board code when flash protection is enabled. In order to use CFI as intended when write protection is disabled, we call the generic flash_init function as defined in drivers/mtd/cfi_flash.c. When protection is enabled we hardcode the geometry info in board code. In order separate our flash_init and the generic flash_init, and be able to call both, we've introduced a new ifdef to cfi_flash.c called CONFIG_CFI_FLASH_OVERRIDE_INIT. Like this:
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diff --git a/drivers/mtd/cfi_flash.c b/drivers/mtd/cfi_flash.c index 6039e1f..772096e 100644 --- a/drivers/mtd/cfi_flash.c +++ b/drivers/mtd/cfi_flash.c @@ -176,6 +176,10 @@ u64 flash_read64(void *addr)__attribute__((weak, alias("__flash_read64"))); #define flash_read64 __flash_read64 #endif
+#ifdef CONFIG_CFI_FLASH_OVERRIDE_INIT +#define flash_init __flash_init +#endif + /*----------------------------------------------------------------------- */ #if defined(CONFIG_ENV_IS_IN_FLASH) || defined(CONFIG_ENV_ADDR_REDUND) || (CONFIG_SYS_MONITOR_BASE >=
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Now, in board code our redefined flash_init will be called. But if write protection is off, we call the original function, eg. __flash_init.
Using the preprocessor is often considered bad design. However, the alternatives here such as adding a weak attribute to flash_init will not make us able to call the generic/original function. Therefore we consider adding an ifdef as better design than making the function weak, and it'll reduce the amount of redundant code in board code.
What do you think about this?
Best regards, Frank E. Svendsbøe