[PATCH v3 3/6] spi: spi-mtk-nor: support 7 bytes transfer of generic spi

[Ikjoon Jang <ikjn@xxxxxxxxxxxx>]

When mtk-nor fallbacks to generic spi transfers, it can actually
transfer up to 7 bytes.

This patch fixes adjust_op_size() and supports_op() to explicitly
check 7 bytes range and also fixes possible under/overflow conditions
in register offsets calculation.

Signed-off-by: Ikjoon Jang <ikjn@xxxxxxxxxxxx>
---

(no changes since v1)

 drivers/spi/spi-mtk-nor.c | 102 ++++++++++++++++++++++++++++----------
 1 file changed, 76 insertions(+), 26 deletions(-)

diff --git a/drivers/spi/spi-mtk-nor.c b/drivers/spi/spi-mtk-nor.c
index 0f7d4ec68730..e7719d249095 100644
--- a/drivers/spi/spi-mtk-nor.c
+++ b/drivers/spi/spi-mtk-nor.c
@@ -79,7 +79,11 @@
 #define MTK_NOR_REG_DMA_DADR		0x720
 #define MTK_NOR_REG_DMA_END_DADR	0x724
 
+/* maximum bytes of TX in PRG mode */
 #define MTK_NOR_PRG_MAX_SIZE		6
+/* maximum bytes of TX + RX is 7, last 1 byte is always being sent as zero */
+#define MTK_NOR_PRG_MAX_CYCLES		7
+
 // Reading DMA src/dst addresses have to be 16-byte aligned
 #define MTK_NOR_DMA_ALIGN		16
 #define MTK_NOR_DMA_ALIGN_MASK		(MTK_NOR_DMA_ALIGN - 1)
@@ -167,6 +171,24 @@ static bool mtk_nor_match_read(const struct spi_mem_op *op)
 	return false;
 }
 
+static bool mtk_nor_check_prg(const struct spi_mem_op *op)
+{
+	size_t len = op->cmd.nbytes + op->addr.nbytes + op->dummy.nbytes;
+
+	if (len > MTK_NOR_PRG_MAX_SIZE)
+		return false;
+
+	if (!op->data.nbytes)
+		return true;
+
+	if (op->data.dir == SPI_MEM_DATA_OUT)
+		return ((len + op->data.nbytes) <= MTK_NOR_PRG_MAX_SIZE);
+	else if (op->data.dir == SPI_MEM_DATA_IN)
+		return ((len + op->data.nbytes) <= MTK_NOR_PRG_MAX_CYCLES);
+	else
+		return true;
+}
+
 static int mtk_nor_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op)
 {
 	size_t len;
@@ -195,10 +217,22 @@ static int mtk_nor_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op)
 		}
 	}
 
-	len = MTK_NOR_PRG_MAX_SIZE - op->cmd.nbytes - op->addr.nbytes -
-	      op->dummy.nbytes;
-	if (op->data.nbytes > len)
-		op->data.nbytes = len;
+	if (mtk_nor_check_prg(op))
+		return 0;
+
+	len = op->cmd.nbytes + op->addr.nbytes + op->dummy.nbytes;
+
+	if (op->data.dir == SPI_MEM_DATA_OUT) {
+		if (len == MTK_NOR_PRG_MAX_SIZE)
+			return -EINVAL;
+		op->data.nbytes = min_t(unsigned int, op->data.nbytes,
+					MTK_NOR_PRG_MAX_SIZE - len);
+	} else  {
+		if (len == MTK_NOR_PRG_MAX_CYCLES)
+			return -EINVAL;
+		op->data.nbytes = min_t(unsigned int, op->data.nbytes,
+					MTK_NOR_PRG_MAX_CYCLES - len);
+	}
 
 	return 0;
 }
@@ -206,8 +240,6 @@ static int mtk_nor_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op)
 static bool mtk_nor_supports_op(struct spi_mem *mem,
 				const struct spi_mem_op *op)
 {
-	size_t len;
-
 	if (op->cmd.buswidth != 1)
 		return false;
 
@@ -223,12 +255,11 @@ static bool mtk_nor_supports_op(struct spi_mem *mem,
 			       (op->data.buswidth == 1);
 	}
 
-	len = op->cmd.nbytes + op->addr.nbytes + op->dummy.nbytes;
-	if ((len > MTK_NOR_PRG_MAX_SIZE) ||
-	    ((op->data.nbytes) && (len == MTK_NOR_PRG_MAX_SIZE)))
+	/* fallback to generic spi xfer */
+	if (op->cmd.buswidth > 1 || op->addr.buswidth > 1 || op->data.buswidth > 1)
 		return false;
 
-	return true;
+	return mtk_nor_check_prg(op);
 }
 
 static void mtk_nor_setup_bus(struct mtk_nor *sp, const struct spi_mem_op *op)
@@ -459,22 +490,36 @@ static int mtk_nor_transfer_one_message(struct spi_controller *master,
 	int stat = 0;
 	int reg_offset = MTK_NOR_REG_PRGDATA_MAX;
 	void __iomem *reg;
-	const u8 *txbuf;
-	u8 *rxbuf;
-	int i;
+	int i, tx_len = 0, rx_len = 0;
 
 	list_for_each_entry(t, &m->transfers, transfer_list) {
-		txbuf = t->tx_buf;
-		for (i = 0; i < t->len; i++, reg_offset--) {
+		const u8 *txbuf = t->tx_buf;
+
+		if (!txbuf) {
+			rx_len += t->len;
+			continue;
+		}
+
+		if (rx_len) {
+			stat = -EPROTO;
+			goto msg_done;
+		}
+
+		for (i = 0; i < t->len && reg_offset >= 0; i++, reg_offset--) {
 			reg = sp->base + MTK_NOR_REG_PRGDATA(reg_offset);
-			if (txbuf)
-				writeb(txbuf[i], reg);
-			else
-				writeb(0, reg);
+			writeb(txbuf[i], reg);
+			tx_len++;
 		}
-		trx_len += t->len;
 	}
 
+	while (reg_offset >= 0) {
+		writeb(0, sp->base + MTK_NOR_REG_PRGDATA(reg_offset));
+		reg_offset--;
+	}
+
+	rx_len = min_t(unsigned long, MTK_NOR_PRG_MAX_CYCLES - tx_len, rx_len);
+	trx_len = tx_len + rx_len;
+
 	writel(trx_len * BITS_PER_BYTE, sp->base + MTK_NOR_REG_PRG_CNT);
 
 	stat = mtk_nor_cmd_exec(sp, MTK_NOR_CMD_PROGRAM,
@@ -482,13 +527,18 @@ static int mtk_nor_transfer_one_message(struct spi_controller *master,
 	if (stat < 0)
 		goto msg_done;
 
-	reg_offset = trx_len - 1;
-	list_for_each_entry(t, &m->transfers, transfer_list) {
-		rxbuf = t->rx_buf;
-		for (i = 0; i < t->len; i++, reg_offset--) {
-			reg = sp->base + MTK_NOR_REG_SHIFT(reg_offset);
-			if (rxbuf)
+	if (rx_len > 0) {
+		reg_offset = rx_len - 1;
+		list_for_each_entry(t, &m->transfers, transfer_list) {
+			u8 *rxbuf = t->rx_buf;
+
+			if (!rxbuf)
+				continue;
+
+			for (i = 0; i < t->len && reg_offset >= 0; i++, reg_offset--) {
+				reg = sp->base + MTK_NOR_REG_SHIFT(reg_offset);
 				rxbuf[i] = readb(reg);
+			}
 		}
 	}
 
-- 
2.28.0.681.g6f77f65b4e-goog