mtd: spi-nor: Fix Cadence QSPI page fault kernel panic

From: Thor Thayer <[email protected]>

The current Cadence QSPI driver caused a kernel panic when loading a Root Filesystem from QSPI. The problem was caused by reading more bytes than needed because the QSPI operated on 4 bytes at a time. <snip>

[    7.947754] spi_nor_read[1048]:from 0x037cad74, len 1 [bfe07fff]
[    7.956247] cqspi_read[910]:offset 0x58502516, buffer=bfe07fff
[    7.956247]
[    7.966046] Unable to handle kernel paging request at virtual
address bfe08002
[    7.973239] pgd = eebfc000
[    7.975931] [bfe08002] *pgd=2fffb811, *pte=00000000, *ppte=00000000

</snip>
Notice above how only 1 byte needed to be read but by reading 4 bytes into the end of a mapped page, an unrecoverable page fault occurred.

This patch uses a temporary buffer to hold the 4 bytes read and then copies only the bytes required into the buffer. A min() function is used to limit the length to prevent buffer overflows.

Request testing of this patch on other platforms. This was tested on the Intel Arria10 SoCFPGA DevKit.

---
v2 Changes to only write dangling bytes at end of transfer since
previous patch may have multiple dangling byte transfers.
Remove write patch since no errors reported and write timeout
needs more investigation.
v3 Add Fixes tag Cc-stable tag.

---
 drivers/mtd/spi-nor/cadence-quadspi.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

index 2f3a4d4232b3..c3f7aaa5d18f 100644
@@ -507,7 +507,9 @@ static int cqspi_indirect_read_execute(struct spi_nor *nor, u8 *rxbuf,
 	void __iomem *reg_base = cqspi->iobase;
 	void __iomem *ahb_base = cqspi->ahb_base;
 	unsigned int remaining = n_rx;
+	unsigned int mod_bytes = n_rx % 4;
 	unsigned int bytes_to_read = 0;
+	u8 *rxbuf_end = rxbuf + n_rx;
 	int ret = 0;
 
 	writel(from_addr, reg_base + CQSPI_REG_INDIRECTRDSTARTADDR);

@@ -536,11 +538,24 @@ static int cqspi_indirect_read_execute(struct spi_nor *nor, u8 *rxbuf,
 		}
 
 		while (bytes_to_read != 0) {
+			unsigned int word_remain = round_down(remaining, 4);
+
 			bytes_to_read *= cqspi->fifo_width;
 			bytes_to_read = bytes_to_read > remaining ?
 					remaining : bytes_to_read;
-			ioread32_rep(ahb_base, rxbuf,
-				     DIV_ROUND_UP(bytes_to_read, 4));
+			bytes_to_read = round_down(bytes_to_read, 4);
+			/* Read 4 byte word chunks then single bytes */
+			if (bytes_to_read) {
+				ioread32_rep(ahb_base, rxbuf,
+					     (bytes_to_read / 4));
+			} else if (!word_remain && mod_bytes) {
+				unsigned int temp = ioread32(ahb_base);
+
+				bytes_to_read = mod_bytes;
+				memcpy(rxbuf, &temp, min((unsigned int)
+							 (rxbuf_end - rxbuf),
+							 bytes_to_read));
+			}
 			rxbuf += bytes_to_read;
 			remaining -= bytes_to_read;
 			bytes_to_read = cqspi_get_rd_sram_level(cqspi);

2.7.4

<snip>
Please disregard - the patch version is incorrect. I will fix and resubmit.