[src/trunk]: src/sys/arch/arm/sunxi Initialize TWI clock rate to 100kHz

[jmcneill <jmcneill%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/efe495347e1c
branches:  trunk
changeset: 356672:efe495347e1c
user:      jmcneill <jmcneill%NetBSD.org@localhost>
date:      Sat Oct 07 20:17:38 2017 +0000

description:
Initialize TWI clock rate to 100kHz

diffstat:

 sys/arch/arm/sunxi/sunxi_twi.c |  18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

diffs (46 lines):

diff -r 31d49875e271 -r efe495347e1c sys/arch/arm/sunxi/sunxi_twi.c
--- a/sys/arch/arm/sunxi/sunxi_twi.c    Sat Oct 07 20:02:07 2017 +0000
+++ b/sys/arch/arm/sunxi/sunxi_twi.c    Sat Oct 07 20:17:38 2017 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: sunxi_twi.c,v 1.4 2017/10/02 22:41:25 jmcneill Exp $ */
+/* $NetBSD: sunxi_twi.c,v 1.5 2017/10/07 20:17:38 jmcneill Exp $ */
 
 /*-
  * Copyright (c) 2017 Jared McNeill <jmcneill%invisible.ca@localhost>
@@ -28,7 +28,7 @@
 
 #include <sys/cdefs.h>
 
-__KERNEL_RCSID(0, "$NetBSD: sunxi_twi.c,v 1.4 2017/10/02 22:41:25 jmcneill Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sunxi_twi.c,v 1.5 2017/10/07 20:17:38 jmcneill Exp $");
 
 #include <sys/param.h>
 #include <sys/bus.h>
@@ -42,6 +42,10 @@
 
 #include <dev/fdt/fdtvar.h>
 
+#define        TWI_CCR_REG     0x14
+#define         TWI_CCR_CLK_M  __BITS(6,3)
+#define         TWI_CCR_CLK_N  __BITS(2,0)
+
 static int sunxi_twi_match(device_t, cfdata_t, void *);
 static void sunxi_twi_attach(device_t, device_t, void *);
 
@@ -135,6 +139,16 @@
        prop_dictionary_set_bool(device_properties(self), "iflg-rwc",
            conf->iflg_rwc);
 
+       /*
+        * 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
+        */
+       const u_int m = 11, n = 2;
+       const uint32_t ccr = __SHIFTIN(n, TWI_CCR_CLK_N) |
+                            __SHIFTIN(m, TWI_CCR_CLK_M); 
+       bus_space_write_4(bst, bsh, TWI_CCR_REG, ccr);
+
        gttwsi_attach_subr(self, bst, bsh);
 
        ih = fdtbus_intr_establish(phandle, 0, IPL_VM, 0, gttwsi_intr, sc);