[PATCH] i3c: dw: Use configured rate and bus mode for clock configuration

From: Jeremy Kerr <jk@codeconstruct.com.au>
To: linux-i3c@lists.infradead.org
Cc: linux-aspeed@lists.ozlabs.org, Vitor Soares <ivitro@gmail.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>
Subject: [PATCH] i3c: dw: Use configured rate and bus mode for clock configuration
Date: Thu, 16 Feb 2023 14:20:40 +0800	[thread overview]
Message-ID: <20230216062040.497815-1-jk@codeconstruct.com.au> (raw)

We may have a non-typical i3c rate configured; use this (instead of
the fixed I3C_BUS_TYP_I3C_SCL_RATE) when calculating timing
characteristics. We can also expand the SCL high time based on the
presence/absence of i2c devices.

Also, since we now have bus->mode, use it to determine whether we se up
the BUS_FREE_TIMING register; rather than re-reading
DEV_CTRL_I2C_SLAVE_PRESENT from hardware.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
---
 drivers/i3c/master/dw-i3c-master.c | 44 ++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 14 deletions(-)

diff --git a/drivers/i3c/master/dw-i3c-master.c b/drivers/i3c/master/dw-i3c-master.c
index 51a8608203de..d73d57362b3b 100644
--- a/drivers/i3c/master/dw-i3c-master.c
+++ b/drivers/i3c/master/dw-i3c-master.c
@@ -515,7 +515,8 @@ static void dw_i3c_master_end_xfer_locked(struct dw_i3c_master *master, u32 isr)
 	dw_i3c_master_start_xfer_locked(master);
 }
 
-static int dw_i3c_clk_cfg(struct dw_i3c_master *master)
+static int dw_i3c_clk_cfg(struct dw_i3c_master *master, unsigned long i3c_rate,
+			  bool pure)
 {
 	unsigned long core_rate, core_period;
 	u32 scl_timing;
@@ -527,31 +528,45 @@ static int dw_i3c_clk_cfg(struct dw_i3c_master *master)
 
 	core_period = DIV_ROUND_UP(1000000000, core_rate);
 
-	hcnt = DIV_ROUND_UP(I3C_BUS_THIGH_MAX_NS, core_period) - 1;
-	if (hcnt < SCL_I3C_TIMING_CNT_MIN)
-		hcnt = SCL_I3C_TIMING_CNT_MIN;
+	/* 50% duty cycle */
+	hcnt = DIV_ROUND_UP(core_rate, i3c_rate * 2);
 
-	lcnt = DIV_ROUND_UP(core_rate, I3C_BUS_TYP_I3C_SCL_RATE) - hcnt;
-	if (lcnt < SCL_I3C_TIMING_CNT_MIN)
-		lcnt = SCL_I3C_TIMING_CNT_MIN;
+	/* In shared mode, we limit t_high, so that i3c SCL signalling is
+	 * rejected by the i2c devices' spike filter */
+	if (!pure)
+		hcnt = min_t(u8, hcnt,
+			     DIV_ROUND_UP(I3C_BUS_THIGH_MAX_NS, core_period)) - 1;
+
+	hcnt = max_t(u8, hcnt, SCL_I3C_TIMING_CNT_MIN);
+
+	lcnt = DIV_ROUND_UP(core_rate, i3c_rate) - hcnt;
+	lcnt = max_t(u8, lcnt, SCL_I3C_TIMING_CNT_MIN);
 
 	scl_timing = SCL_I3C_TIMING_HCNT(hcnt) | SCL_I3C_TIMING_LCNT(lcnt);
 	writel(scl_timing, master->regs + SCL_I3C_PP_TIMING);
 
-	if (!(readl(master->regs + DEVICE_CTRL) & DEV_CTRL_I2C_SLAVE_PRESENT))
+	if (pure)
 		writel(BUS_I3C_MST_FREE(lcnt), master->regs + BUS_FREE_TIMING);
 
-	lcnt = DIV_ROUND_UP(I3C_BUS_TLOW_OD_MIN_NS, core_period);
+	/* open drain mode requires a minimum of OD_MIN_NS */
+	lcnt = max_t(u8, lcnt, DIV_ROUND_UP(I3C_BUS_TLOW_OD_MIN_NS, core_period));
 	scl_timing = SCL_I3C_TIMING_HCNT(hcnt) | SCL_I3C_TIMING_LCNT(lcnt);
 	writel(scl_timing, master->regs + SCL_I3C_OD_TIMING);
 
-	lcnt = DIV_ROUND_UP(core_rate, I3C_BUS_SDR1_SCL_RATE) - hcnt;
+	/* Timings for lower SDRx rates where specified by device MXDS values;
+	 * we limit these to the global max rate provided, which also prevents
+	 * weird duty cycles */
+	lcnt = max_t(u8, lcnt,
+		     DIV_ROUND_UP(core_rate, I3C_BUS_SDR1_SCL_RATE) - hcnt);
 	scl_timing = SCL_EXT_LCNT_1(lcnt);
-	lcnt = DIV_ROUND_UP(core_rate, I3C_BUS_SDR2_SCL_RATE) - hcnt;
+	lcnt = max_t(u8, lcnt,
+		     DIV_ROUND_UP(core_rate, I3C_BUS_SDR2_SCL_RATE) - hcnt);
 	scl_timing |= SCL_EXT_LCNT_2(lcnt);
-	lcnt = DIV_ROUND_UP(core_rate, I3C_BUS_SDR3_SCL_RATE) - hcnt;
+	lcnt = max_t(u8, lcnt,
+		     DIV_ROUND_UP(core_rate, I3C_BUS_SDR3_SCL_RATE) - hcnt);
 	scl_timing |= SCL_EXT_LCNT_3(lcnt);
-	lcnt = DIV_ROUND_UP(core_rate, I3C_BUS_SDR4_SCL_RATE) - hcnt;
+	lcnt = max_t(u8, lcnt,
+		     DIV_ROUND_UP(core_rate, I3C_BUS_SDR4_SCL_RATE) - hcnt);
 	scl_timing |= SCL_EXT_LCNT_4(lcnt);
 	writel(scl_timing, master->regs + SCL_EXT_LCNT_TIMING);
 
@@ -605,7 +620,8 @@ static int dw_i3c_master_bus_init(struct i3c_master_controller *m)
 			return ret;
 		fallthrough;
 	case I3C_BUS_MODE_PURE:
-		ret = dw_i3c_clk_cfg(master);
+		ret = dw_i3c_clk_cfg(master, bus->scl_rate.i3c,
+				     bus->mode == I3C_BUS_MODE_PURE);
 		if (ret)
 			return ret;
 		break;
-- 
2.39.1


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