From 486c150478777ef53cfef6f0d46840b9406b0612 Mon Sep 17 00:00:00 2001
From: Gabor Juhos <juhosg@openwrt.org>
Date: Thu, 27 Dec 2012 10:42:24 +0100
Subject: [PATCH] spi/ath79: add delay between SCK changes

commit 440114fdb13cbc53ea734bcc05b86bcf5b1e430c upstream.

The driver uses the "as fast as it can" approach
to drive the SCK signal. However this does not
work with certain low speed SPI chips (e.g. the
PCF2123 RTC chip).

The patch adds per-bit slowdowns in order to be
able to use the driver with such chips as well.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
---
 drivers/spi/spi-ath79.c |   44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

--- a/drivers/spi/spi-ath79.c
+++ b/drivers/spi/spi-ath79.c
@@ -24,17 +24,24 @@
 #include <linux/spi/spi_bitbang.h>
 #include <linux/bitops.h>
 #include <linux/gpio.h>
+#include <linux/clk.h>
+#include <linux/err.h>
 
 #include <asm/mach-ath79/ar71xx_regs.h>
 #include <asm/mach-ath79/ath79_spi_platform.h>
 
 #define DRV_NAME	"ath79-spi"
 
+#define ATH79_SPI_RRW_DELAY_FACTOR	12000
+#define MHZ				(1000 * 1000)
+
 struct ath79_spi {
 	struct spi_bitbang	bitbang;
 	u32			ioc_base;
 	u32			reg_ctrl;
 	void __iomem		*base;
+	struct clk		*clk;
+	unsigned		rrw_delay;
 };
 
 static inline u32 ath79_spi_rr(struct ath79_spi *sp, unsigned reg)
@@ -52,6 +59,12 @@ static inline struct ath79_spi *ath79_sp
 	return spi_master_get_devdata(spi->master);
 }
 
+static inline void ath79_spi_delay(struct ath79_spi *sp, unsigned nsecs)
+{
+	if (nsecs > sp->rrw_delay)
+		ndelay(nsecs - sp->rrw_delay);
+}
+
 static void ath79_spi_chipselect(struct spi_device *spi, int is_active)
 {
 	struct ath79_spi *sp = ath79_spidev_to_sp(spi);
@@ -184,7 +197,9 @@ static u32 ath79_spi_txrx_mode0(struct s
 
 		/* setup MSB (to slave) on trailing edge */
 		ath79_spi_wr(sp, AR71XX_SPI_REG_IOC, out);
+		ath79_spi_delay(sp, nsecs);
 		ath79_spi_wr(sp, AR71XX_SPI_REG_IOC, out | AR71XX_SPI_IOC_CLK);
+		ath79_spi_delay(sp, nsecs);
 
 		word <<= 1;
 	}
@@ -198,6 +213,7 @@ static int ath79_spi_probe(struct platfo
 	struct ath79_spi *sp;
 	struct ath79_spi_platform_data *pdata;
 	struct resource	*r;
+	unsigned long rate;
 	int ret;
 
 	master = spi_alloc_master(&pdev->dev, sizeof(*sp));
@@ -236,12 +252,36 @@ static int ath79_spi_probe(struct platfo
 		goto err_put_master;
 	}
 
+	sp->clk = clk_get(&pdev->dev, "ahb");
+	if (IS_ERR(sp->clk)) {
+		ret = PTR_ERR(sp->clk);
+		goto err_unmap;
+	}
+
+	ret = clk_enable(sp->clk);
+	if (ret)
+		goto err_clk_put;
+
+	rate = DIV_ROUND_UP(clk_get_rate(sp->clk), MHZ);
+	if (!rate) {
+		ret = -EINVAL;
+		goto err_clk_disable;
+	}
+
+	sp->rrw_delay = ATH79_SPI_RRW_DELAY_FACTOR / rate;
+	dev_dbg(&pdev->dev, "register read/write delay is %u nsecs\n",
+		sp->rrw_delay);
+
 	ret = spi_bitbang_start(&sp->bitbang);
 	if (ret)
-		goto err_unmap;
+		goto err_clk_disable;
 
 	return 0;
 
+err_clk_disable:
+	clk_disable(sp->clk);
+err_clk_put:
+	clk_put(sp->clk);
 err_unmap:
 	iounmap(sp->base);
 err_put_master:
@@ -256,6 +296,8 @@ static int ath79_spi_remove(struct platf
 	struct ath79_spi *sp = platform_get_drvdata(pdev);
 
 	spi_bitbang_stop(&sp->bitbang);
+	clk_disable(sp->clk);
+	clk_put(sp->clk);
 	iounmap(sp->base);
 	platform_set_drvdata(pdev, NULL);
 	spi_master_put(sp->bitbang.master);