[U-Boot] [PATCH] spi: cadence_qspi_apb: Use 32 bit indirect write transaction when possible

[Vignesh R]

According to Section 11.15.4.9.2 Indirect Write Controller of K2G SoC
TRM SPRUHY8D[1], the external master is only permitted to issue 32-bit
data interface writes until the last word of an indirect transfer
otherwise indirect writes is known to fails sometimes. So, make sure
that QSPI indirect writes are 32 bit sized except for the last write.

[1]www.ti.com/lit/ug/spruhy8d/spruhy8d.pdf

Signed-off-by: Vignesh R <vigneshr at ti.com>
---
 drivers/spi/cadence_qspi_apb.c | 41 +++++++++++++++++++++++++++++++----------
 1 file changed, 31 insertions(+), 10 deletions(-)

diff --git a/drivers/spi/cadence_qspi_apb.c b/drivers/spi/cadence_qspi_apb.c
index e285d3c1e761..0115700ef6a7 100644
--- a/drivers/spi/cadence_qspi_apb.c
+++ b/drivers/spi/cadence_qspi_apb.c
@@ -739,23 +739,44 @@ int cadence_qspi_apb_indirect_write_execute(struct cadence_spi_platdata *plat,
 {
 	unsigned int page_size = plat->page_size;
 	unsigned int remaining = n_tx;
-	unsigned int write_bytes;
+	unsigned int write_bytes = 0;
 	int ret;
 
+	/* Handle non-4-byte aligned access to avoid data abort. */
+	if ((uintptr_t) txbuf % 4) {
+		write_bytes = n_tx > 3 ? 4 - ((uintptr_t)txbuf % 4) : n_tx;
+		/* Configure the indirect read transfer bytes */
+		writel(write_bytes, plat->regbase + CQSPI_REG_INDIRECTWRBYTES);
+		/* Start the indirect write transfer */
+		writel(CQSPI_REG_INDIRECTWR_START_MASK,
+		       plat->regbase + CQSPI_REG_INDIRECTWR);
+		writesb(plat->ahbbase, txbuf, write_bytes);
+		txbuf += write_bytes;
+		remaining -= write_bytes;
+		if (remaining > 0) {
+			u32 start_addr = readl(plat->regbase +
+					       CQSPI_REG_INDIRECTWRSTARTADDR);
+			start_addr += write_bytes;
+			writel(start_addr, plat->regbase +
+			       CQSPI_REG_INDIRECTWRSTARTADDR);
+		}
+	}
+
 	/* Configure the indirect read transfer bytes */
-	writel(n_tx, plat->regbase + CQSPI_REG_INDIRECTWRBYTES);
+	writel(n_tx - write_bytes, plat->regbase + CQSPI_REG_INDIRECTWRBYTES);
 
-	/* Start the indirect write transfer */
-	writel(CQSPI_REG_INDIRECTWR_START_MASK,
-	       plat->regbase + CQSPI_REG_INDIRECTWR);
+	if (remaining > 0)
+		writel(CQSPI_REG_INDIRECTWR_START_MASK,
+		       plat->regbase + CQSPI_REG_INDIRECTWR);
 
 	while (remaining > 0) {
 		write_bytes = remaining > page_size ? page_size : remaining;
-		/* Handle non-4-byte aligned access to avoid data abort. */
-		if (((uintptr_t)txbuf % 4) || (write_bytes % 4))
-			writesb(plat->ahbbase, txbuf, write_bytes);
-		else
-			writesl(plat->ahbbase, txbuf, write_bytes >> 2);
+
+		writesl(plat->ahbbase, txbuf, write_bytes >> 2);
+		if (write_bytes % 4)
+			writesb(plat->ahbbase,
+				txbuf + rounddown(write_bytes, 4),
+				write_bytes % 4);
 
 		ret = wait_for_bit("QSPI", plat->regbase + CQSPI_REG_SDRAMLEVEL,
 				   CQSPI_REG_SDRAMLEVEL_WR_MASK <<
-- 
2.10.2