clk: bcm2835: Add support for setting leaf clock rates while running.

As long as you wait for !BUSY, you can do glitch-free updates of clock
rate while the clock is running.

Signed-off-by: Eric Anholt <eric@anholt.net>

diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
index 0c2a6bc..3be10be 100644 (file)
--- a/drivers/clk/bcm/clk-bcm2835.c
+++ b/drivers/clk/bcm/clk-bcm2835.c
@@ -1098,15 +1098,19 @@ static int bcm2835_clock_set_rate(struct clk_hw *hw,
 
        spin_lock(&cprman->regs_lock);
 
-       /*
-        * Setting up frac support
-        *
-        * In principle it is recommended to stop/start the clock first,
-        * but as we set CLK_SET_RATE_GATE during registration of the
-        * clock this requirement should be take care of by the
-        * clk-framework.
+       ctl = cprman_read(cprman, data->ctl_reg);
+
+       /* If the clock is running, we have to pause clock generation while
+        * updating the control and div regs.  This is glitchless (no clock
+        * signals generated faster than the rate) but each reg access is two
+        * OSC cycles so the clock will slow down for a moment.
         */
-       ctl = cprman_read(cprman, data->ctl_reg) & ~CM_FRAC;
+       if (ctl & CM_ENABLE) {
+               cprman_write(cprman, data->ctl_reg, ctl & ~CM_ENABLE);
+               bcm2835_clock_wait_busy(clock);
+       }
+
+       ctl &= ~CM_FRAC;
        ctl |= (div & CM_DIV_FRAC_MASK) ? CM_FRAC : 0;
        cprman_write(cprman, data->ctl_reg, ctl);
 
@@ -1476,7 +1480,7 @@ static struct clk_hw *bcm2835_register_clock(struct bcm2835_cprman *cprman,
                init.ops = &bcm2835_vpu_clock_clk_ops;
        } else {
                init.ops = &bcm2835_clock_clk_ops;
-               init.flags |= CLK_SET_RATE_GATE | CLK_SET_PARENT_GATE;
+               init.flags |= CLK_SET_PARENT_GATE;
 
                /* If the clock wasn't actually enabled at boot, it's not
                 * critical.