Fix variable CPU clock for MPC859/866 systems for low CPU clocks

CHANGELOG

@@ -2,6 +2,8 @@
 Changes since U-Boot 1.0.1:
 ======================================================================
 
+* Fix variable CPU clock for MPC859/866 systems for low CPU clocks
+
 * Implement adaptive SDRAM timing configuration based on actual CPU
   clock frequency for INCA-IP; fix problem with board hanging when
   switching from 150MHz to 100MHz

README

@@ -415,12 +415,28 @@ The following options need to be configured:
 		Define exactly one of
 		CONFIG_MPC8240, CONFIG_MPC8245
 
-- 8xx CPU Options: (if using an 8xx cpu)
+- 8xx CPU Options: (if using an MPC8xx cpu)
 		Define one or more of
 		CONFIG_8xx_GCLK_FREQ	- if get_gclk_freq() cannot work
 					  e.g. if there is no 32KHz
 					  reference PIT/RTC clock
 
+- 859/866 CPU options: (if using a MPC859 or MPC866 CPU):
+		CFG_866_OSCCLK
+		CFG_866_CPUCLK_MIN
+		CFG_866_CPUCLK_MAX
+		CFG_866_CPUCLK_DEFAULT
+			See doc/README.MPC866
+
+		CFG_MEASURE_CPUCLK
+
+                Define this to measure the actual CPU clock instead
+                of relying on the correctness of the configured
+                values. Mostly useful for board bringup to make sure
+                the PLL is locked at the intended frequency. Note
+                that this requires a (stable) reference clock (32 kHz
+                RTC clock),
+
 - Linux Kernel Interface:
 		CONFIG_CLOCKS_IN_MHZ
 

board/tqm8xx/tqm8xx.c

@@ -128,14 +128,6 @@ int checkboard (void)
 			break;
 		putc (*s);
 	}
-#if defined(CFG_866_CPUCLK_MIN) && defined(CFG_866_CPUCLK_MAX)
-	printf ("  [%d.%d...%d.%d MHz]",
-		CFG_866_CPUCLK_MIN / 1000000,
-		((CFG_866_CPUCLK_MIN % 1000000) + 50000) / 100000,
-		CFG_866_CPUCLK_MAX / 1000000,
-		((CFG_866_CPUCLK_MAX % 1000000) + 50000) / 100000
-	);
-#endif
 	putc ('\n');
 
 	return (0);

cpu/mpc8xx/cpu.c

@@ -123,10 +123,22 @@ static int check_CPU (long clock, uint pvr, uint immr)
 	else
 		printf ("unknown M%s (0x%08x)", id_str, k);
 
-	printf (" at %s MHz:", strmhz (buf, clock));
 
-	printf (" %u kB I-Cache", checkicache () >> 10);
+#if defined(CFG_866_CPUCLK_MIN) && defined(CFG_866_CPUCLK_MAX)
-	printf (" %u kB D-Cache", checkdcache () >> 10);
+	printf (" at %s MHz [%d.%d...%d.%d MHz]\n       ",
+		strmhz (buf, clock),
+		CFG_866_CPUCLK_MIN / 1000000,
+		((CFG_866_CPUCLK_MIN % 1000000) + 50000) / 100000,
+		CFG_866_CPUCLK_MAX / 1000000,
+		((CFG_866_CPUCLK_MAX % 1000000) + 50000) / 100000
+	);
+#else
+	printf (" at %s MHz: ", strmhz (buf, clock));
+#endif
+	printf ("%u kB I-Cache %u kB D-Cache",
+		checkicache () >> 10,
+		checkdcache () >> 10
+	);
 
 	/* do we have a FEC (860T/P or 852/859/866)? */
 

cpu/mpc8xx/serial.c

@@ -71,11 +71,11 @@
 static void serial_setdivisor(volatile cpm8xx_t *cp)
 {
 	DECLARE_GLOBAL_DATA_PTR;
-	int divisor=gd->cpu_clk/16/gd->baudrate;
+	int divisor=(gd->cpu_clk + 8*gd->baudrate)/16/gd->baudrate;
 
 	if(divisor/16>0x1000) {
 		/* bad divisor, assume 50Mhz clock and 9600 baud */
-		divisor=(50*1000*1000)/16/9600;
+		divisor=(50*1000*1000 + 8*9600)/16/9600;
 	}
 
 #ifdef CFG_BRGCLK_PRESCALE

cpu/mpc8xx/speed.c

@@ -25,7 +25,7 @@
 #include <mpc8xx.h>
 #include <asm/processor.h>
 
-#ifndef CONFIG_TQM866M
+#if !defined(CONFIG_TQM866M) || defined(CFG_MEASURE_CPUCLK)
 
 #define PITC_SHIFT 16
 #define PITR_SHIFT 16
@@ -170,6 +170,10 @@ unsigned long measure_gclk(void)
 #endif
 }
 
+#endif
+
+#if !defined(CONFIG_TQM866M)
+
 /*
  * get_clocks() fills in gd->cpu_clock depending on CONFIG_8xx_GCLK_FREQ
  * or (if it is not defined) measure_gclk() (which uses the ref clock)
@@ -230,6 +234,9 @@ int get_clocks_866 (void)
 		cpuclk = CFG_866_CPUCLK_DEFAULT;
 
 	gd->cpu_clk = init_pll_866 (cpuclk);
+#if defined(CFG_MEASURE_CPUCLK)
+	gd->cpu_clk = measure_gclk ();
+#endif
 
 	if ((immr->im_clkrst.car_sccr & SCCR_EBDF11) == 0)
 		gd->bus_clk = gd->cpu_clk;
@@ -269,8 +276,19 @@ static long init_pll_866 (long clk)
 	char              mfi, mfn, mfd, s, pdf;
 	long              step_mfi, step_mfn;
 
-	pdf = 0;
+	if (clk < 20000000) {
-	if (clk < 80000000) {
+		clk *= 2;
+		pdf = 1;
+	} else {
+		pdf = 0;
+	}
+
+	if (clk < 40000000) {
+		s = 2;
+		step_mfi = CFG_866_OSCCLK / 4;
+		mfd = 7;
+		step_mfn = CFG_866_OSCCLK / 30;
+	} else if (clk < 80000000) {
 		s = 1;
 		step_mfi = CFG_866_OSCCLK / 2;
 		mfd = 14;
@@ -294,13 +312,14 @@ static long init_pll_866 (long clk)
 
 	/* Calculate effective clk
 	 */
-	n = (mfi * step_mfi) + (mfn * step_mfn);
+	n = ((mfi * step_mfi) + (mfn * step_mfn)) / (pdf + 1);
 
 	immr->im_clkrstk.cark_plprcrk = KAPWR_KEY;
 
 	plprcr = (immr->im_clkrst.car_plprcr & ~(PLPRCR_MFN_MSK
 			| PLPRCR_MFD_MSK | PLPRCR_S_MSK
-			| PLPRCR_MFI_MSK | PLPRCR_DBRMO))
+			| PLPRCR_MFI_MSK | PLPRCR_DBRMO
+			| PLPRCR_PDF_MSK))
 			| (mfn << PLPRCR_MFN_SHIFT)
 			| (mfd << PLPRCR_MFD_SHIFT)
 			| (s << PLPRCR_S_SHIFT)

doc/README.MPC866

@@ -12,6 +12,10 @@ If the "cpuclk" environment variable value is within the CPUCLK_MIN /
 CPUCLK_MAX limits, the specified value is used. Otherwise, the
 default CPU clock value is set.
 
+Please make sure you understand what you are doing, and understand
+the restrictions of your hardware (board, processor). For example,
+ethernet will stop working for CPU clock frequencies below 25 MHz.
+
 Please note that for now the new clock-handling code has been enabled
 for the TQM866M board only, even though it should be pretty much
 common for other MPC859 / MPC866 based boards also. Our intention

include/configs/TQM866M.h

@@ -37,12 +37,19 @@
 #define CONFIG_TQM866M		1	/* ...on a TQM8xxM module	*/
 
 #define CFG_866_OSCCLK		 10000000	/*  10 MHz - PLL input clock		*/
-#define CFG_866_CPUCLK_MIN	 10000000	/*  10 MHz - CPU minimum clock		*/
+#define CFG_866_CPUCLK_MIN	 15000000	/*  15 MHz - CPU minimum clock		*/
 #define CFG_866_CPUCLK_MAX	133000000	/* 133 MHz - CPU maximum clock		*/
 #define CFG_866_CPUCLK_DEFAULT	 50000000	/*  50 MHz - CPU default clock		*/
 						/* (it will be used if there is no	*/
 						/* 'cpuclk' variable with valid value)	*/
 
+#undef CFG_MEASURE_CPUCLK			/* Measure real cpu clock	*/
+						/* (function measure_gclk()	*/
+						/* will be called)		*/
+#ifdef CFG_MEASURE_CPUCLK
+#define CFG_8XX_XIN		10000000	/* measure_gclk() needs this	*/
+#endif
+
 #define CONFIG_8xx_CONS_SMC1	1	/* Console is on SMC1		*/
 
 #define CONFIG_BAUDRATE		115200	/* console baudrate = 115kbps	*/