mtd: spi-nor: fsl-quadspi: Don't let -EINVAL on the bus

fsl_qspi_get_seqid() may return -EINVAL, but fsl_qspi_init_ahb_read()
doesn't check for error codes with the result that -EINVAL could find
itself signalled over the bus.

In conjunction with the LS1046A SoC's A-009283 errata
("Illegal accesses to SPI flash memory can result in a system hang")
this illegal access to SPI flash memory results in a system hang
if userspace attempts reading later on.

Avoid this by always checking fsl_qspi_get_seqid()'s return value
and bail out otherwise.

Fixes: e46ecda7 ("mtd: spi-nor: Add Freescale QuadSPI driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>

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

@@ -543,6 +543,9 @@ fsl_qspi_runcmd(struct fsl_qspi *q, u8 cmd, unsigned int addr, int len)
 
 	/* trigger the LUT now */
 	seqid = fsl_qspi_get_seqid(q, cmd);
+	if (seqid < 0)
+		return seqid;
+
 	qspi_writel(q, (seqid << QUADSPI_IPCR_SEQID_SHIFT) | len,
 			base + QUADSPI_IPCR);
 
@@ -671,7 +674,7 @@ static void fsl_qspi_set_map_addr(struct fsl_qspi *q)
  * causes the controller to clear the buffer, and use the sequence pointed
  * by the QUADSPI_BFGENCR[SEQID] to initiate a read from the flash.
  */
-static void fsl_qspi_init_ahb_read(struct fsl_qspi *q)
+static int fsl_qspi_init_ahb_read(struct fsl_qspi *q)
 {
 	void __iomem *base = q->iobase;
 	int seqid;
@@ -696,8 +699,13 @@ static void fsl_qspi_init_ahb_read(struct fsl_qspi *q)
 
 	/* Set the default lut sequence for AHB Read. */
 	seqid = fsl_qspi_get_seqid(q, q->nor[0].read_opcode);
+	if (seqid < 0)
+		return seqid;
+
 	qspi_writel(q, seqid << QUADSPI_BFGENCR_SEQID_SHIFT,
 		q->iobase + QUADSPI_BFGENCR);
+
+	return 0;
 }
 
 /* This function was used to prepare and enable QSPI clock */
@@ -805,9 +813,7 @@ static int fsl_qspi_nor_setup_last(struct fsl_qspi *q)
 	fsl_qspi_init_lut(q);
 
 	/* Init for AHB read */
-	fsl_qspi_init_ahb_read(q);
-
-	return 0;
+	return fsl_qspi_init_ahb_read(q);
 }
 
 static const struct of_device_id fsl_qspi_dt_ids[] = {