From 22e63ff3a23d189187d96dbcec50e94233027b3a Mon Sep 17 00:00:00 2001
From: Phil Edworthy <PHIL.EDWORTHY@renesas.com>
Date: Tue, 29 Nov 2016 12:58:33 +0000
Subject: [PATCH] spi: cadence_qspi: Fix CS timings

The Cadence QSPI controller has specified overheads for the various CS
times that are in addition to those programmed in to the Device Delay
register. The overheads are different for the delays.

In addition, the existing code does not handle the case when the delay
is less than a SCLK period.

This change accurately calculates the additional delays in Ref clocks.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
---
 drivers/spi/cadence_qspi_apb.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/spi/cadence_qspi_apb.c b/drivers/spi/cadence_qspi_apb.c
index 39e31f618c..df6a91fc9f 100644
--- a/drivers/spi/cadence_qspi_apb.c
+++ b/drivers/spi/cadence_qspi_apb.c
@@ -169,9 +169,6 @@
 	((readl(base + CQSPI_REG_CONFIG) >>		\
 		CQSPI_REG_CONFIG_IDLE_LSB) & 0x1)
 
-#define CQSPI_CAL_DELAY(tdelay_ns, tref_ns, tsclk_ns)		\
-	((((tdelay_ns) - (tsclk_ns)) / (tref_ns)))
-
 #define CQSPI_GET_RD_SRAM_LEVEL(reg_base)			\
 	(((readl(reg_base + CQSPI_REG_SDRAMLEVEL)) >>	\
 	CQSPI_REG_SDRAMLEVEL_RD_LSB) & CQSPI_REG_SDRAMLEVEL_RD_MASK)
@@ -355,16 +352,20 @@ void cadence_qspi_apb_delay(void *reg_base,
 	cadence_qspi_apb_controller_disable(reg_base);
 
 	/* Convert to ns. */
-	ref_clk_ns = (1000000000) / ref_clk;
+	ref_clk_ns = DIV_ROUND_UP(1000000000, ref_clk);
 
 	/* Convert to ns. */
-	sclk_ns = (1000000000) / sclk_hz;
-
-	/* Plus 1 to round up 1 clock cycle. */
-	tshsl = CQSPI_CAL_DELAY(tshsl_ns, ref_clk_ns, sclk_ns) + 1;
-	tchsh = CQSPI_CAL_DELAY(tchsh_ns, ref_clk_ns, sclk_ns) + 1;
-	tslch = CQSPI_CAL_DELAY(tslch_ns, ref_clk_ns, sclk_ns) + 1;
-	tsd2d = CQSPI_CAL_DELAY(tsd2d_ns, ref_clk_ns, sclk_ns) + 1;
+	sclk_ns = DIV_ROUND_UP(1000000000, sclk_hz);
+
+	/* The controller adds additional delay to that programmed in the reg */
+	if (tshsl_ns >= sclk_ns + ref_clk_ns)
+		tshsl_ns -= sclk_ns + ref_clk_ns;
+	if (tchsh_ns >= sclk_ns + 3 * ref_clk_ns)
+		tchsh_ns -= sclk_ns + 3 * ref_clk_ns;
+	tshsl = DIV_ROUND_UP(tshsl_ns, ref_clk_ns);
+	tchsh = DIV_ROUND_UP(tchsh_ns, ref_clk_ns);
+	tslch = DIV_ROUND_UP(tslch_ns, ref_clk_ns);
+	tsd2d = DIV_ROUND_UP(tsd2d_ns, ref_clk_ns);
 
 	reg = ((tshsl & CQSPI_REG_DELAY_TSHSL_MASK)
 			<< CQSPI_REG_DELAY_TSHSL_LSB);
-- 
2.39.5