[PATCH] ioc4: PCI bus speed detection

Several hardware features of SGI's IOC4 I/O controller chip require
timing-related driver calculations dependent upon the PCI bus speed.  This
patch enables the core IOC4 driver code to detect the actual bus speed and
store a value that can later be used by the IOC4 subdrivers as needed.

Signed-off-by: Brent Casavant <bcasavan@sgi.com>
Acked-by: Pat Gefre <pfg@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 128 insertions, 0 deletions

diff --git a/drivers/sn/ioc4.c b/drivers/sn/ioc4.c
index 70862d72ea9d..ea75b3d0612b 100644
--- a/drivers/sn/ioc4.c
+++ b/drivers/sn/ioc4.c
@@ -29,7 +29,26 @@
 #include <linux/module.h>
 #include <linux/pci.h>
 #include <linux/ioc4.h>
+#include <linux/mmtimer.h>
+#include <linux/rtc.h>
 #include <linux/rwsem.h>
+#include <asm/sn/addrs.h>
+#include <asm/sn/clksupport.h>
+#include <asm/sn/shub_mmr.h>
+
+/***************
+ * Definitions *
+ ***************/
+
+/* Tweakable values */
+
+/* PCI bus speed detection/calibration */
+#define IOC4_CALIBRATE_COUNT 63 /* Calibration cycle period */
+#define IOC4_CALIBRATE_CYCLES 256       /* Average over this many cycles */
+#define IOC4_CALIBRATE_DISCARD 2        /* Discard first few cycles */
+#define IOC4_CALIBRATE_LOW_MHZ 25       /* Lower bound on bus speed sanity */
+#define IOC4_CALIBRATE_HIGH_MHZ 75      /* Upper bound on bus speed sanity */
+#define IOC4_CALIBRATE_DEFAULT_MHZ 66   /* Assumed if sanity check fails */
 
 /************************
  * Submodule management *
@@ -101,6 +120,112 @@ ioc4_unregister_submodule(struct ioc4_submodule *is)
  * Device management *
  *********************/
 
+#define IOC4_CALIBRATE_LOW_LIMIT \
+        (1000*IOC4_EXTINT_COUNT_DIVISOR/IOC4_CALIBRATE_LOW_MHZ)
+#define IOC4_CALIBRATE_HIGH_LIMIT \
+        (1000*IOC4_EXTINT_COUNT_DIVISOR/IOC4_CALIBRATE_HIGH_MHZ)
+#define IOC4_CALIBRATE_DEFAULT \
+        (1000*IOC4_EXTINT_COUNT_DIVISOR/IOC4_CALIBRATE_DEFAULT_MHZ)
+
+#define IOC4_CALIBRATE_END \
+        (IOC4_CALIBRATE_CYCLES + IOC4_CALIBRATE_DISCARD)
+
+#define IOC4_INT_OUT_MODE_TOGGLE 0x7    /* Toggle INT_OUT every COUNT+1 ticks */
+
+/* Determines external interrupt output clock period of the PCI bus an
+ * IOC4 is attached to.  This value can be used to determine the PCI
+ * bus speed.
+ *
+ * IOC4 has a design feature that various internal timers are derived from
+ * the PCI bus clock.  This causes IOC4 device drivers to need to take the
+ * bus speed into account when setting various register values (e.g. INT_OUT
+ * register COUNT field, UART divisors, etc).  Since this information is
+ * needed by several subdrivers, it is determined by the main IOC4 driver,
+ * even though the following code utilizes external interrupt registers
+ * to perform the speed calculation.
+ */
+static void
+ioc4_clock_calibrate(struct ioc4_driver_data *idd)
+{
+        extern unsigned long sn_rtc_cycles_per_second;
+        union ioc4_int_out int_out;
+        union ioc4_gpcr gpcr;
+        unsigned int state, last_state = 1;
+        uint64_t start = 0, end, period;
+        unsigned int count = 0;
+
+        /* Enable output */
+        gpcr.raw = 0;
+        gpcr.fields.dir = IOC4_GPCR_DIR_0;
+        gpcr.fields.int_out_en = 1;
+        writel(gpcr.raw, &idd->idd_misc_regs->gpcr_s.raw);
+
+        /* Reset to power-on state */
+        writel(0, &idd->idd_misc_regs->int_out.raw);
+        mmiowb();
+
+        printk(KERN_INFO
+               "%s: Calibrating PCI bus speed "
+               "for pci_dev %s ... ", __FUNCTION__, pci_name(idd->idd_pdev));
+        /* Set up square wave */
+        int_out.raw = 0;
+        int_out.fields.count = IOC4_CALIBRATE_COUNT;
+        int_out.fields.mode = IOC4_INT_OUT_MODE_TOGGLE;
+        int_out.fields.diag = 0;
+        writel(int_out.raw, &idd->idd_misc_regs->int_out.raw);
+        mmiowb();
+
+        /* Check square wave period averaged over some number of cycles */
+        do {
+                int_out.raw = readl(&idd->idd_misc_regs->int_out.raw);
+                state = int_out.fields.int_out;
+                if (!last_state && state) {
+                        count++;
+                        if (count == IOC4_CALIBRATE_END) {
+                                end = rtc_time();
+                                break;
+                        } else if (count == IOC4_CALIBRATE_DISCARD)
+                                start = rtc_time();
+                }
+                last_state = state;
+        } while (1);
+
+        /* Calculation rearranged to preserve intermediate precision.
+         * Logically:
+         * 1. "end - start" gives us number of RTC cycles over all the
+         *    square wave cycles measured.
+         * 2. Divide by number of square wave cycles to get number of
+         *    RTC cycles per square wave cycle.
+         * 3. Divide by 2*(int_out.fields.count+1), which is the formula
+         *    by which the IOC4 generates the square wave, to get the
+         *    number of RTC cycles per IOC4 INT_OUT count.
+         * 4. Divide by sn_rtc_cycles_per_second to get seconds per
+         *    count.
+         * 5. Multiply by 1E9 to get nanoseconds per count.
+         */
+        period = ((end - start) * 1000000000) /
+            (IOC4_CALIBRATE_CYCLES * 2 * (IOC4_CALIBRATE_COUNT + 1)
+             * sn_rtc_cycles_per_second);
+
+        /* Bounds check the result. */
+        if (period > IOC4_CALIBRATE_LOW_LIMIT ||
+            period < IOC4_CALIBRATE_HIGH_LIMIT) {
+                printk("failed. Assuming PCI clock ticks are %d ns.\n",
+                       IOC4_CALIBRATE_DEFAULT / IOC4_EXTINT_COUNT_DIVISOR);
+                period = IOC4_CALIBRATE_DEFAULT;
+        } else {
+                printk("succeeded. PCI clock ticks are %ld ns.\n",
+                       period / IOC4_EXTINT_COUNT_DIVISOR);
+        }
+
+        /* Remember results.  We store the extint clock period rather
+         * than the PCI clock period so that greater precision is
+         * retained.  Divide by IOC4_EXTINT_COUNT_DIVISOR to get
+         * PCI clock period.
+         */
+        idd->count_period = period;
+}
+
 /* Adds a new instance of an IOC4 card */
 static int
 ioc4_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id)
@@ -170,6 +295,9 @@ ioc4_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id)
         pci_write_config_dword(idd->idd_pdev, PCI_COMMAND,
                                pcmd | PCI_COMMAND_PARITY | PCI_COMMAND_SERR);
 
+        /* Determine PCI clock */
+        ioc4_clock_calibrate(idd);
+
         /* Disable/clear all interrupts.  Need to do this here lest
          * one submodule request the shared IOC4 IRQ, but interrupt
          * is generated by a different subdevice.