mtd: spi-nor: cadence-quadspi: Fix direct mode write timeouts

Sometimes when writing large size files to flash in direct/memory mapped
mode, it is seen that flash write enable command times out with error:
[  503.146293] cadence-qspi 47040000.ospi: Flash command execution timed out.

This is because, we need to make sure previous direct write operation
is complete by polling for IDLE bit in CONFIG_REG before starting the
next operation.

Fix this by polling for IDLE bit after memory mapped write.

Fixes: a27f2eaf ("mtd: spi-nor: cadence-quadspi: Add support for direct access mode")
Cc: stable@vger.kernel.org
Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>

drivers/mtd/spi-nor/cadence-quadspi.c

@@ -926,10 +926,12 @@ static ssize_t cqspi_write(struct spi_nor *nor, loff_t to,
 	if (ret)
 		return ret;
 
-	if (f_pdata->use_direct_mode)
+	if (f_pdata->use_direct_mode) {
 		memcpy_toio(cqspi->ahb_base + to, buf, len);
-	else
+		ret = cqspi_wait_idle(cqspi);
+	} else {
 		ret = cqspi_indirect_write_execute(nor, to, buf, len);
+	}
 	if (ret)
 		return ret;