[PATCH v3 2/2] i2c: dwsignware: determine HS tHIGH and tLOW based on HW parameters

[Michael Wu]

In commit 35eba185fd1a ("i2c: designware: Calculate SCL timing parameter
for High Speed Mode") hs_hcnt and hs_lcnt are calculated based on fixed
tHIGH = 160 and tLOW = 120. However, the set of these fixed values only
applies to the combination of hardware parameters IC_CAP_LOADING = 400pF
and IC_CLK_FREQ_OPTIMIZATION = 1. Outside of this combination, if these
fixed tHIGH = 160 and tLOW = 120 are still used, the calculated hs_hcnt
and hs_lcnt may not be small enough, making it impossible for the SCL
frequency to reach 3.4 MHz.

Section 3.15.4.5 in DesignWare DW_apb_i2b Databook v2.03 says that when
IC_CLK_FREQ_OPTIMIZATION = 0,

    MIN_SCL_HIGHtime = 60 ns for 3.4 Mbps, bus loading = 100pF
		     = 120 ns for 3.4 Mbps, bus loading = 400pF
    MIN_SCL_LOWtime = 160 ns for 3.4 Mbps, bus loading = 100pF
		    = 320 ns for 3.4 Mbps, bus loading = 400pF

and section 3.15.4.6 says that when IC_CLK_FREQ_OPTIMIZATION = 1,

    MIN_SCL_HIGHtime = 60 ns for 3.4 Mbps, bus loading = 100pF
		     = 160 ns for 3.4 Mbps, bus loading = 400pF
    MIN_SCL_LOWtime = 120 ns for 3.4 Mbps, bus loading = 100pF
		    = 320 ns for 3.4 Mbps, bus loading = 400pF

In order to calculate more accurate hs_hcnt amd hs_lcnt, two hardware
parameters IC_CAP_LOADING and IC_CLK_FREQ_OPTIMIZATION must be
considered together.

Signed-off-by: Michael Wu <michael.wu@xxxxxxxxx>
---
 drivers/i2c/busses/i2c-designware-common.c |  5 +++++
 drivers/i2c/busses/i2c-designware-core.h   |  5 +++++
 drivers/i2c/busses/i2c-designware-master.c | 23 ++++++++++++++++++++--
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
index 080204182bb5..9599be1de775 100644
--- a/drivers/i2c/busses/i2c-designware-common.c
+++ b/drivers/i2c/busses/i2c-designware-common.c
@@ -380,6 +380,11 @@ int i2c_dw_fw_parse_and_configure(struct dw_i2c_dev *dev)
 
 	i2c_parse_fw_timings(device, t, false);
 
+	if (device_property_read_u32(device, "snps,bus-capacitance-pf", &dev->bus_capacitance_pf))
+		dev->bus_capacitance_pf = 100;
+
+	dev->clk_freq_optimized = device_property_read_bool(device, "snps,clk-freq-optimized");
+
 	i2c_dw_adjust_bus_speed(dev);
 
 	if (is_of_node(fwnode))
diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index 1ac2afd03a0a..44c97bf15843 100644
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -240,6 +240,9 @@ struct reset_control;
  * @set_sda_hold_time: callback to retrieve IP specific SDA hold timing
  * @mode: operation mode - DW_IC_MASTER or DW_IC_SLAVE
  * @rinfo: I²C GPIO recovery information
+ * @bus_capacitance_pf: bus capacitance in picofarads
+ * @clk_freq_optimized: indicate whether hardware input clock frequency is
+ *	reduced by reducing the internal latency
  *
  * HCNT and LCNT parameters can be used if the platform knows more accurate
  * values than the one computed based only on the input clock frequency.
@@ -297,6 +300,8 @@ struct dw_i2c_dev {
 	int			(*set_sda_hold_time)(struct dw_i2c_dev *dev);
 	int			mode;
 	struct i2c_bus_recovery_info rinfo;
+	u32			bus_capacitance_pf;
+	bool			clk_freq_optimized;
 };
 
 #define ACCESS_INTR_MASK			BIT(0)
diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
index e46f1b22c360..3dbc94db94a4 100644
--- a/drivers/i2c/busses/i2c-designware-master.c
+++ b/drivers/i2c/busses/i2c-designware-master.c
@@ -154,12 +154,31 @@ static int i2c_dw_set_timings_master(struct dw_i2c_dev *dev)
 			dev->hs_hcnt = 0;
 			dev->hs_lcnt = 0;
 		} else if (!dev->hs_hcnt || !dev->hs_lcnt) {
+			u32 t_high, t_low;
+
+			/*
+			 * The legal values stated in the databook for bus
+			 * capacitance are only 100pF and 400pF.
+			 * If dev->bus_capacitance_pf is greater than or equals
+			 * to 400, t_high and t_low are assumed to be
+			 * appropriate values for 400pF, otherwise 100pF.
+			 */
+			if (dev->bus_capacitance_pf >= 400) {
+				/* assume bus capacitance is 400pF */
+				t_high = dev->clk_freq_optimized ? 160 : 120;
+				t_low = 320;
+			} else {
+				/* assume bus capacitance is 100pF */
+				t_high = 60;
+				t_low = dev->clk_freq_optimized ? 120 : 160;
+			}
+
 			ic_clk = i2c_dw_clk_rate(dev);
 			dev->hs_hcnt =
 				i2c_dw_scl_hcnt(dev,
 						DW_IC_HS_SCL_HCNT,
 						ic_clk,
-						160,	/* tHIGH = 160 ns */
+						t_high,
 						sda_falling_time,
 						0,	/* DW default */
 						0);	/* No offset */
@@ -167,7 +186,7 @@ static int i2c_dw_set_timings_master(struct dw_i2c_dev *dev)
 				i2c_dw_scl_lcnt(dev,
 						DW_IC_HS_SCL_LCNT,
 						ic_clk,
-						320,	/* tLOW = 320 ns */
+						t_low,
 						scl_falling_time,
 						0);	/* No offset */
 		}
-- 
2.43.0