linux-kernel - [PATCH v2] i3c: master: svc: adjust SDR according to i3c spec

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Message-Id: <20240718091329.3788619-1-carlos.song@nxp.com>
Date: Thu, 18 Jul 2024 17:13:28 +0800
From: carlos.song@....com
To: miquel.raynal@...tlin.com,
	conor.culhane@...vaco.com,
	alexandre.belloni@...tlin.com,
	frank.li@....com
Cc: linux-i3c@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-imx@....com
Subject: [PATCH v2] i3c: master: svc: adjust SDR according to i3c spec

From: Carlos Song <carlos.song@....com>

According to I3C Specification(Version 1.1) 5.1.2.4 "Use of Clock
Speed to Prevent Legacy I2C Devices From Seeing I3C traffic", when
slow i2c devices(FM/FM+ rate i2c frequency without 50ns filter)
works on i3c bus, i3c SDR should work at FM/FM+ rate.

Adjust timing for difference mode.

Signed-off-by: Clark Wang <xiaoning.wang@....com>
Signed-off-by: Carlos Song <carlos.song@....com>
Reviewed-by: Frank Li <frank.li@....com>
---
Change for V2:
- Correct I3C clk configuration and simplify the code:
  Pure I3C mode and MIXED-FAST I3C mode just use the same i3c clk configuration:
  1. i3c push-pull timing is 40ns high and 40ns low at 12.5Mhz
  2. i3c open-darin timing is 40ns high and 200ns low at ~4Mhz
  3. i2cbaud should be different between Pure I3C mode and MIXED-FAST
     I3C mode.
---
 drivers/i3c/master/svc-i3c-master.c | 31 ++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
index e80c002991f7..78116530f431 100644
--- a/drivers/i3c/master/svc-i3c-master.c
+++ b/drivers/i3c/master/svc-i3c-master.c
@@ -127,6 +127,8 @@
 
 /* This parameter depends on the implementation and may be tuned */
 #define SVC_I3C_FIFO_SIZE 16
+#define SVC_I3C_PPBAUD_MAX 15
+#define SVC_I3C_QUICK_I2C_CLK 4170000
 
 #define SVC_I3C_EVENT_IBI	BIT(0)
 #define SVC_I3C_EVENT_HOTJOIN	BIT(1)
@@ -535,6 +537,7 @@ static int svc_i3c_master_bus_init(struct i3c_master_controller *m)
 	struct i3c_bus *bus = i3c_master_get_bus(m);
 	struct i3c_device_info info = {};
 	unsigned long fclk_rate, fclk_period_ns;
+	unsigned long i2c_period_ns, i2c_scl_rate, i3c_scl_rate;
 	unsigned int high_period_ns, od_low_period_ns;
 	u32 ppbaud, pplow, odhpp, odbaud, odstop, i2cbaud, reg;
 	int ret;
@@ -555,12 +558,15 @@ static int svc_i3c_master_bus_init(struct i3c_master_controller *m)
 	}
 
 	fclk_period_ns = DIV_ROUND_UP(1000000000, fclk_rate);
+	i2c_period_ns = DIV_ROUND_UP(1000000000, bus->scl_rate.i2c);
+	i2c_scl_rate = bus->scl_rate.i2c;
+	i3c_scl_rate = bus->scl_rate.i3c;
 
 	/*
 	 * Using I3C Push-Pull mode, target is 12.5MHz/80ns period.
 	 * Simplest configuration is using a 50% duty-cycle of 40ns.
 	 */
-	ppbaud = DIV_ROUND_UP(40, fclk_period_ns) - 1;
+	ppbaud = DIV_ROUND_UP(fclk_rate / 2, i3c_scl_rate) - 1;
 	pplow = 0;
 
 	/*
@@ -570,7 +576,7 @@ static int svc_i3c_master_bus_init(struct i3c_master_controller *m)
 	 */
 	odhpp = 1;
 	high_period_ns = (ppbaud + 1) * fclk_period_ns;
-	odbaud = DIV_ROUND_UP(240 - high_period_ns, high_period_ns) - 1;
+	odbaud = DIV_ROUND_UP(fclk_rate, SVC_I3C_QUICK_I2C_CLK * (1 + ppbaud)) - 2;
 	od_low_period_ns = (odbaud + 1) * high_period_ns;
 
 	switch (bus->mode) {
@@ -579,20 +585,27 @@ static int svc_i3c_master_bus_init(struct i3c_master_controller *m)
 		odstop = 0;
 		break;
 	case I3C_BUS_MODE_MIXED_FAST:
-	case I3C_BUS_MODE_MIXED_LIMITED:
 		/*
 		 * Using I2C Fm+ mode, target is 1MHz/1000ns, the difference
 		 * between the high and low period does not really matter.
 		 */
-		i2cbaud = DIV_ROUND_UP(1000, od_low_period_ns) - 2;
+		i2cbaud = DIV_ROUND_UP(i2c_period_ns, od_low_period_ns) - 2;
 		odstop = 1;
 		break;
+	case I3C_BUS_MODE_MIXED_LIMITED:
 	case I3C_BUS_MODE_MIXED_SLOW:
-		/*
-		 * Using I2C Fm mode, target is 0.4MHz/2500ns, with the same
-		 * constraints as the FM+ mode.
-		 */
-		i2cbaud = DIV_ROUND_UP(2500, od_low_period_ns) - 2;
+		/* I3C PP + I3C OP + I2C OP both use i2c clk rate */
+		if (ppbaud > SVC_I3C_PPBAUD_MAX) {
+			ppbaud = SVC_I3C_PPBAUD_MAX;
+			pplow =  DIV_ROUND_UP(fclk_rate, i3c_scl_rate) - (2 + 2 * ppbaud);
+		}
+
+		high_period_ns = (ppbaud + 1) * fclk_period_ns;
+		odhpp = 0;
+		odbaud = DIV_ROUND_UP(fclk_rate, i2c_scl_rate * (2 + 2 * ppbaud)) - 1;
+
+		od_low_period_ns = (odbaud + 1) * high_period_ns;
+		i2cbaud = DIV_ROUND_UP(i2c_period_ns, od_low_period_ns) - 2;
 		odstop = 1;
 		break;
 	default:
-- 
2.34.1