Set the proper bus clock rate based on the "clock-frequency" property and

the rate of the parent clock.  If the "clock-frequency" property isn't
present, use the default standard mode clock of 100kHz.

diff --git a/sys/dev/fdt/sxitwi.c b/sys/dev/fdt/sxitwi.c
index 98eae99..e972348 100644 (file)
--- a/sys/dev/fdt/sxitwi.c
+++ b/sys/dev/fdt/sxitwi.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sxitwi.c,v 1.6 2018/01/05 12:46:13 kettenis Exp $ */
+/* $OpenBSD: sxitwi.c,v 1.7 2018/01/06 11:23:14 kettenis Exp $ */
 /*     $NetBSD: gttwsi_core.c,v 1.2 2014/11/23 13:37:27 jmcneill Exp $ */
 /*
  * Copyright (c) 2008 Eiji Kawauchi.
@@ -180,12 +180,35 @@ sxitwi_attach(struct device *parent, struct device *self, void *aux)
        struct sxitwi_softc *sc = (struct sxitwi_softc *)self;
        struct fdt_attach_args *faa = aux;
        struct i2cbus_attach_args iba;
+       uint32_t freq, parent_freq;
+       uint32_t m, n;
 
        if (faa->fa_nreg < 1) {
                printf(": no registers\n");
                return;
        }
 
+       /*
+        * Calculate clock dividers up front such that we can bail out
+        * early if the desired clock rate can't be obtained.  Make
+        * sure the bus clock rate is never above the desired rate.
+        */
+       parent_freq = clock_get_frequency(faa->fa_node, NULL);
+       freq = OF_getpropint(faa->fa_node, "clock-frequency", 100000);
+       if (parent_freq == 0) {
+               printf(": unknown clock frequency\n");
+               return;
+       }
+       n = 0, m = 0;
+       while ((freq * (1 << n) * 16 * 10) < parent_freq)
+               n++;
+       while ((freq * (1 << n) * (m + 1) * 10) < parent_freq)
+               m++;
+       if (n > 8 || m > 16) {
+               printf(": clock frequency too high\n");
+               return;
+       }
+
        sc->sc_node = faa->fa_node;
        sc->sc_iot = faa->fa_iot;
 
@@ -222,12 +245,8 @@ sxitwi_attach(struct device *parent, struct device *self, void *aux)
        clock_enable(faa->fa_node, NULL);
        reset_deassert_all(faa->fa_node);
 
-       /*
-        * Set clock rate to 100kHz. From the datasheet:
-        *   For 100Khz standard speed 2Wire, CLK_N=2, CLK_M=11
-        *   F0=48M/2^2=12Mhz, F1=F0/(10*(11+1)) = 0.1Mhz
-        */
-       sxitwi_write_4(sc, TWI_CCR_REG, (11 << 3) | (2 << 0));
+       /* Set clock rate. */
+       sxitwi_write_4(sc, TWI_CCR_REG, (m << 3) | (n << 0));
 
        /* Put the controller into Soft Reset. */
        sxitwi_write_4(sc, TWSI_SOFTRESET, SOFTRESET_VAL);