spi: spi-nxp-fspi: Add support for IP read only

Add support for disabling AHB bus and read entire flash contents via IP
bus only. Please note, this enables IP bus read using a quirk which can
be enabled directly in device-type data or in existence of an errata
where AHB bus may need to be disabled.
Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Link: https://lore.kernel.org/r/20210302124936.1972546-2-kuldeep.singh@nxp.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-nxp-fspi.c

@@ -311,6 +311,9 @@
 #define NXP_FSPI_MAX_CHIPSELECT		4
 #define NXP_FSPI_MIN_IOMAP	SZ_4M
 
+/* Access flash memory using IP bus only */
+#define FSPI_QUIRK_USE_IP_ONLY	BIT(0)
+
 struct nxp_fspi_devtype_data {
 	unsigned int rxfifo;
 	unsigned int txfifo;
@@ -359,6 +362,11 @@ struct nxp_fspi {
 	int selected;
 };
 
+static inline int needs_ip_only(struct nxp_fspi *f)
+{
+	return f->devtype_data->quirks & FSPI_QUIRK_USE_IP_ONLY;
+}
+
 /*
  * R/W functions for big- or little-endian registers:
  * The FSPI controller's endianness is independent of
@@ -553,8 +561,8 @@ static void nxp_fspi_prepare_lut(struct nxp_fspi *f,
 	for (i = 0; i < ARRAY_SIZE(lutval); i++)
 		fspi_writel(f, lutval[i], base + FSPI_LUT_REG(i));
 
-	dev_dbg(f->dev, "CMD[%x] lutval[0:%x \t 1:%x \t 2:%x \t 3:%x]\n",
-		op->cmd.opcode, lutval[0], lutval[1], lutval[2], lutval[3]);
+	dev_dbg(f->dev, "CMD[%x] lutval[0:%x \t 1:%x \t 2:%x \t 3:%x], size: 0x%08x\n",
+		op->cmd.opcode, lutval[0], lutval[1], lutval[2], lutval[3], op->data.nbytes);
 
 	/* lock LUT */
 	fspi_writel(f, FSPI_LUTKEY_VALUE, f->iobase + FSPI_LUTKEY);
@@ -852,12 +860,14 @@ static int nxp_fspi_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
 
 	nxp_fspi_prepare_lut(f, op);
 	/*
-	 * If we have large chunks of data, we read them through the AHB bus
-	 * by accessing the mapped memory. In all other cases we use
-	 * IP commands to access the flash.
+	 * If we have large chunks of data, we read them through the AHB bus by
+	 * accessing the mapped memory. In all other cases we use IP commands
+	 * to access the flash. Read via AHB bus may be corrupted due to
+	 * existence of an errata and therefore discard AHB read in such cases.
 	 */
 	if (op->data.nbytes > (f->devtype_data->rxfifo - 4) &&
-	    op->data.dir == SPI_MEM_DATA_IN) {
+	    op->data.dir == SPI_MEM_DATA_IN &&
+	    !needs_ip_only(f)) {
 		err = nxp_fspi_read_ahb(f, op);
 	} else {
 		if (op->data.nbytes && op->data.dir == SPI_MEM_DATA_OUT)
@@ -888,6 +898,12 @@ static int nxp_fspi_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op)
 			op->data.nbytes = ALIGN_DOWN(op->data.nbytes, 8);
 	}
 
+	/* Limit data bytes to RX FIFO in case of IP read only */
+	if (op->data.dir == SPI_MEM_DATA_IN &&
+	    needs_ip_only(f) &&
+	    op->data.nbytes > f->devtype_data->rxfifo)
+		op->data.nbytes = f->devtype_data->rxfifo;
+
 	return 0;
 }