Error while erasing external QSPI flash with nordic,qspi-nor driver

[dpkristensen]

I have found a bug in SDK v2.6.0 at zephyr/drivers/flash/nrf_qspi_nor.c while erasing the external MX25R64 flash.

Environment:

• nRF5340 DK Hardware (MX25R64 external flash over QSPI with nordic,qspi-nor driver)
• NCS SDK v2.6.0 (sdk-zephyr tag v3.5.99-ncs1)

I have a custom project which uses the FLASH_MAP API to erase the external flash in a loop at 64KB increments (offsets: 0x0, 0x10000, etc...). The first one succeeds, but the second one fails at offset 0x10000. I am pretty sure this is a timing issue. This does NOT occur on the nRF7002 DK, which communicates to the same flash chip via SPI instead of QSPI (which also uses the generic JEDEC compatibility SPI NOR driver instead of a Nordic driver).

I tracked the failure down to zephyr/drivers/flash/nrf_qspi_nor.c:qspi_nor_write_protection_set() on the call using SPI_NOR_CMD_WREN. There's a couple issues with the function:

• The return code from qspi_send_cmd() is ignored and replaced with -EIO in all failure cases; this makes it impossible to distinguish the root cause.
• In the problem case, qspi_send_cmd() returns -EBUSY; so this means the chip is likely not ready for the operation to be performed yet.

The core of the issue is that the function does not block the caller until the erase operation is complete, so this means the next operation could fail if it happens too soon. I think the driver should query the WEL bit in the status register after the command has been sent to verify the status is updated (From the data sheet, the Write Status Register Cycle time is ~10ms up to 20ms max).

Workaround

Apparently the workaround some other people have been using is to set CONFIG_NORDIC_QSPI_NOR_TIMEOUT_MS to a higher value, such as 2000; but this is not the ideal solution because it is never clear how long it will actually take.

The workaround I am using for this issue is to do the erase in a loop as long as it is returning -EIO:

        unsigned int attempts = 3;
        while(attempts) {
            err = flash_area_erase(fa, offset, erase_size);
            if(err == -EIO) {
                --attempts;
            } else {
                // Stop on success or other error.
                break;
            }
        }

Additional Info

I had created the issue originally at https://devzone.nordicsemi.com/f/nordic-q-a/111056/error-while-erasing-external-qspi-flash-with-nordic-qspi-nor-driver and Nordic support suggested I open one here as well. Please see this thread for more info.

[nordic-piks]

Triaged internally

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