i2c: designware: Support non-standard bus speeds

Add support for non-standard bus speeds by treating them as detuned
versions of the slowest standard speed not less than the requested
speed.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
index 35f7628..45cbd91 100644 (file)
--- a/drivers/i2c/busses/i2c-designware-common.c
+++ b/drivers/i2c/busses/i2c-designware-common.c
@@ -318,6 +318,9 @@ void i2c_dw_adjust_bus_speed(struct dw_i2c_dev *dev)
 {
        u32 acpi_speed = i2c_dw_acpi_round_bus_speed(dev->dev);
        struct i2c_timings *t = &dev->timings;
+       u32 wanted_speed;
+       u32 legal_speed = 0;
+       int i;
 
        /*
         * Find bus speed from the "clock-frequency" device property, ACPI
@@ -329,6 +332,30 @@ void i2c_dw_adjust_bus_speed(struct dw_i2c_dev *dev)
                t->bus_freq_hz = max(t->bus_freq_hz, acpi_speed);
        else
                t->bus_freq_hz = I2C_MAX_FAST_MODE_FREQ;
+
+       wanted_speed = t->bus_freq_hz;
+
+       /* For unsupported speeds, scale down the lowest speed which is faster. */
+       for (i = 0; i < ARRAY_SIZE(supported_speeds); i++) {
+               /* supported speeds is in decreasing order */
+               if (wanted_speed == supported_speeds[i]) {
+                       legal_speed = 0;
+                       break;
+               }
+               if (wanted_speed > supported_speeds[i])
+                       break;
+
+               legal_speed = supported_speeds[i];
+       }
+
+       if (legal_speed) {
+               /*
+                * Pretend this was the requested speed, but preserve the preferred
+                * speed so the clock counts can be scaled.
+                */
+               t->bus_freq_hz = legal_speed;
+               dev->wanted_bus_speed = wanted_speed;
+       }
 }
 EXPORT_SYMBOL_GPL(i2c_dw_adjust_bus_speed);
 

diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index 2762c3e..1529679 100644 (file)
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -291,6 +291,7 @@ struct dw_i2c_dev {
        u16                     fp_lcnt;
        u16                     hs_hcnt;
        u16                     hs_lcnt;
+       u32                     wanted_bus_speed;
        int                     (*acquire_lock)(void);
        void                    (*release_lock)(void);
        int                     semaphore_idx;

diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
index 50604b6..d04a3a1 100644 (file)
--- a/drivers/i2c/busses/i2c-designware-master.c
+++ b/drivers/i2c/busses/i2c-designware-master.c
@@ -41,7 +41,7 @@ static void i2c_dw_configure_fifo_master(struct dw_i2c_dev *dev)
 static u16 clock_calc(struct dw_i2c_dev *dev, bool want_high)
 {
        struct i2c_timings *t = &dev->timings;
-       u32 wanted_speed = t->bus_freq_hz;
+       u32 wanted_speed = dev->wanted_bus_speed ?: t->bus_freq_hz;
        u32 clk_khz = i2c_dw_clk_rate(dev);
        u32 extra_ns = want_high ? t->scl_fall_ns : t->scl_rise_ns;
        u32 extra_cycles = (u32)((u64)clk_khz * extra_ns / 1000000);