i3c: master: dw: stop hardcoding initial speed

Bus-speed could be default(12.5MHz) or defined by users in dts.
Dw-i3c-master should not hard-code the initial speed to be
I3C_BUS_TYP_I3C_SCL_RATE (12.5MHz)
And because of Synopsys's I3C controller limit (hcnt/lcnt register
length) and core-clk provided, there is a limit to bus speed, too.
For example, when core-clk is 250 MHz, the bus speed cannot be
lowered below 1MHz.

Tested: tested with an i3c sensor and captured with a logic analyzer.

Signed-off-by: Jack Chen <zenghuchen@google.com>
Link: https://lore.kernel.org/r/20230216151057.293764-1-zenghuchen@google.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/i3c/master/dw-i3c-master.c

@@ -531,7 +531,7 @@ static int dw_i3c_clk_cfg(struct dw_i3c_master *master)
 	if (hcnt < SCL_I3C_TIMING_CNT_MIN)
 		hcnt = SCL_I3C_TIMING_CNT_MIN;
 
-	lcnt = DIV_ROUND_UP(core_rate, I3C_BUS_TYP_I3C_SCL_RATE) - hcnt;
+	lcnt = DIV_ROUND_UP(core_rate, master->base.bus.scl_rate.i3c) - hcnt;
 	if (lcnt < SCL_I3C_TIMING_CNT_MIN)
 		lcnt = SCL_I3C_TIMING_CNT_MIN;
 
@@ -541,7 +541,8 @@ static int dw_i3c_clk_cfg(struct dw_i3c_master *master)
 	if (!(readl(master->regs + DEVICE_CTRL) & DEV_CTRL_I2C_SLAVE_PRESENT))
 		writel(BUS_I3C_MST_FREE(lcnt), master->regs + BUS_FREE_TIMING);
 
-	lcnt = DIV_ROUND_UP(I3C_BUS_TLOW_OD_MIN_NS, core_period);
+	lcnt = max_t(u8,
+		     DIV_ROUND_UP(I3C_BUS_TLOW_OD_MIN_NS, core_period), lcnt);
 	scl_timing = SCL_I3C_TIMING_HCNT(hcnt) | SCL_I3C_TIMING_LCNT(lcnt);
 	writel(scl_timing, master->regs + SCL_I3C_OD_TIMING);