[PATCH 1/4] i2c: at91: add upport for the HOLD field

[Ludovic Desroches]

The hold field allows to configure the data hold time which can be set
with the help of the generic binding 'i2c-sda-hold-time-ns'. This
feature has been introduced with SAMA5D4 SoC family.

Signed-off-by: Ludovic Desroches <ludovic.desroches at atmel.com>
---
 drivers/i2c/busses/i2c-at91.c | 54 ++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 51 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
index 10835d1..09e1690 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 */
@@ -110,6 +111,7 @@ struct at91_twi_pdata {
 	unsigned clk_offset;
 	bool has_unre_flag;
 	bool has_alt_cmd;
+	bool has_hold_field;
 	struct at_dma_slave dma_slave;
 };
 
@@ -187,10 +189,13 @@ static void at91_init_twi_bus(struct at91_twi_dev *dev)
  */
 static void at91_calc_twi_clock(struct at91_twi_dev *dev, int twi_clk)
 {
-	int ckdiv, cdiv, div;
+	int ckdiv, cdiv, div, hold = 0;
 	struct at91_twi_pdata *pdata = dev->pdata;
 	int offset = pdata->clk_offset;
 	int max_ckdiv = pdata->clk_max_div;
+	u32 twd_hold_time_ns = 0;
+
+#define MAX_HOLD 31
 
 	div = max(0, (int)DIV_ROUND_UP(clk_get_rate(dev->clk),
 				       2 * twi_clk) - offset);
@@ -204,8 +209,33 @@ 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_dbg(dev->dev, "cdiv %d ckdiv %d\n", cdiv, ckdiv);
+	if (pdata->has_hold_field) {
+		of_property_read_u32(dev->dev->of_node, "i2c-sda-hold-time-ns",
+				     &twd_hold_time_ns);
+
+		/*
+		 * hold time = HOLD + 3 x T_peripheral_clock
+		 * Use clk rate in kHz to prevent overflows when computing
+		 * hold.
+		 */
+		hold = DIV_ROUND_UP(twd_hold_time_ns
+				    * (clk_get_rate(dev->clk) / 1000), 1000000);
+		hold -= 3;
+		if (hold < 0)
+			hold = 0;
+		if (hold > MAX_HOLD) {
+			dev_warn(dev->dev,
+				 "HOLD field set to its maximum value (%d instead of %d)\n",
+				 MAX_HOLD, hold);
+			hold = MAX_HOLD;
+		}
+	}
+
+	dev->twi_cwgr_reg = (ckdiv << 16) | (cdiv << 8) | cdiv
+			    | AT91_TWI_CWGR_HOLD(hold);
+
+	dev_dbg(dev->dev, "cdiv %d ckdiv %d hold %d (%d ns)\n",
+		cdiv, ckdiv, hold, twd_hold_time_ns);
 }
 
 static void at91_twi_dma_cleanup(struct at91_twi_dev *dev)
@@ -797,6 +827,7 @@ static struct at91_twi_pdata at91rm9200_config = {
 	.clk_offset = 3,
 	.has_unre_flag = true,
 	.has_alt_cmd = false,
+	.has_hold_field = false,
 };
 
 static struct at91_twi_pdata at91sam9261_config = {
@@ -804,6 +835,7 @@ static struct at91_twi_pdata at91sam9261_config = {
 	.clk_offset = 4,
 	.has_unre_flag = false,
 	.has_alt_cmd = false,
+	.has_hold_field = false,
 };
 
 static struct at91_twi_pdata at91sam9260_config = {
@@ -811,6 +843,7 @@ static struct at91_twi_pdata at91sam9260_config = {
 	.clk_offset = 4,
 	.has_unre_flag = false,
 	.has_alt_cmd = false,
+	.has_hold_field = false,
 };
 
 static struct at91_twi_pdata at91sam9g20_config = {
@@ -818,6 +851,7 @@ static struct at91_twi_pdata at91sam9g20_config = {
 	.clk_offset = 4,
 	.has_unre_flag = false,
 	.has_alt_cmd = false,
+	.has_hold_field = false,
 };
 
 static struct at91_twi_pdata at91sam9g10_config = {
@@ -825,6 +859,7 @@ static struct at91_twi_pdata at91sam9g10_config = {
 	.clk_offset = 4,
 	.has_unre_flag = false,
 	.has_alt_cmd = false,
+	.has_hold_field = false,
 };
 
 static const struct platform_device_id at91_twi_devtypes[] = {
@@ -854,6 +889,15 @@ static struct at91_twi_pdata at91sam9x5_config = {
 	.clk_offset = 4,
 	.has_unre_flag = false,
 	.has_alt_cmd = false,
+	.has_hold_field = false,
+};
+
+static struct at91_twi_pdata sama5d4_config = {
+	.clk_max_div = 7,
+	.clk_offset = 4,
+	.has_unre_flag = false,
+	.has_alt_cmd = false,
+	.has_hold_field = true,
 };
 
 static struct at91_twi_pdata sama5d2_config = {
@@ -861,6 +905,7 @@ static struct at91_twi_pdata sama5d2_config = {
 	.clk_offset = 4,
 	.has_unre_flag = true,
 	.has_alt_cmd = true,
+	.has_hold_field = true,
 };
 
 static const struct of_device_id atmel_twi_dt_ids[] = {
@@ -883,6 +928,9 @@ static const struct of_device_id atmel_twi_dt_ids[] = {
 		.compatible = "atmel,at91sam9x5-i2c",
 		.data = &at91sam9x5_config,
 	}, {
+		.compatible = "atmel,sama5d4-i2c",
+		.data = &sama5d4_config,
+	}, {
 		.compatible = "atmel,sama5d2-i2c",
 		.data = &sama5d2_config,
 	}, {
-- 
2.5.0