linux-kernel - [PATCH 1/2] i2c: at91: add DT property for the HOLD field of TWIHS

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Message-ID: <1443602831-27069-1-git-send-email-ludovic.desroches@atmel.com>
Date:	Wed, 30 Sep 2015 10:47:10 +0200
From:	Ludovic Desroches <ludovic.desroches@...el.com>
To:	<wsa@...-dreams.de>
CC:	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <nicolas.ferre@...el.com>,
	Wenyou Yang <wenyou.yang@...el.com>,
	Ludovic Desroches <ludovic.desroches@...el.com>
Subject: [PATCH 1/2] i2c: at91: add DT property for the HOLD field of TWIHS_CWGR

From: Wenyou Yang <wenyou.yang@...el.com>

Add the HOLD field setting in order to support I2C slave devices which need
a longer hold time of the data.
Since it depends on the slave devices connected to the bus, add a DT
property "atmel,twd-hold-cycles" to specify this HOLD field.

Signed-off-by: Wenyou Yang <wenyou.yang@...el.com>
Signed-off-by: Ludovic Desroches <ludovic.desroches@...el.com>
---
 drivers/i2c/busses/i2c-at91.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
index 1c758cd..06e66ef 100644
--- a/drivers/i2c/busses/i2c-at91.c
+++ b/drivers/i2c/busses/i2c-at91.c
@@ -64,6 +64,7 @@
 #define	AT91_TWI_IADR		0x000c	/* Internal Address Register */
 
 #define	AT91_TWI_CWGR		0x0010	/* Clock Waveform Generator Reg */
+#define	AT91_TWI_CWGR_HOLD(x)	(((x) & 0x1f) << 24)
 
 #define	AT91_TWI_SR		0x0020	/* Status Register */
 #define	AT91_TWI_TXCOMP		BIT(0)	/* Transmission Complete */
@@ -185,7 +186,8 @@ static void at91_init_twi_bus(struct at91_twi_dev *dev)
  * Calculate symmetric clock as stated in datasheet:
  * twi_clk = F_MAIN / (2 * (cdiv * (1 << ckdiv) + offset))
  */
-static void at91_calc_twi_clock(struct at91_twi_dev *dev, int twi_clk)
+static void at91_calc_twi_clock(struct at91_twi_dev *dev,
+				int twi_clk, u32 twd_hold)
 {
 	int ckdiv, cdiv, div;
 	struct at91_twi_pdata *pdata = dev->pdata;
@@ -204,7 +206,9 @@ static void at91_calc_twi_clock(struct at91_twi_dev *dev, int twi_clk)
 		cdiv = 255;
 	}
 
-	dev->twi_cwgr_reg = (ckdiv << 16) | (cdiv << 8) | cdiv;
+	dev->twi_cwgr_reg = (ckdiv << 16) | (cdiv << 8) | cdiv
+			    | AT91_TWI_CWGR_HOLD(twd_hold);
+
 	dev_dbg(dev->dev, "cdiv %d ckdiv %d\n", cdiv, ckdiv);
 }
 
@@ -936,6 +940,7 @@ static int at91_twi_probe(struct platform_device *pdev)
 	int rc;
 	u32 phy_addr;
 	u32 bus_clk_rate;
+	u32 twd_hold_cycles;
 
 	dev = devm_kzalloc(&pdev->dev, sizeof(*dev), GFP_KERNEL);
 	if (!dev)
@@ -992,7 +997,12 @@ static int at91_twi_probe(struct platform_device *pdev)
 	if (rc)
 		bus_clk_rate = DEFAULT_TWI_CLK_HZ;
 
-	at91_calc_twi_clock(dev, bus_clk_rate);
+	rc = of_property_read_u32(dev->dev->of_node,
+				  "atmel,twd-hold-cycles", &twd_hold_cycles);
+	if (rc)
+		twd_hold_cycles = 0;
+
+	at91_calc_twi_clock(dev, bus_clk_rate, twd_hold_cycles);
 	at91_init_twi_bus(dev);
 
 	snprintf(dev->adapter.name, sizeof(dev->adapter.name), "AT91");
-- 
2.5.0

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