hw/misc/bcm2835_cprman: implement PLL channels behaviour

A PLL channel is able to further divide the generated PLL frequency.
The divider is given in the CTRL_A2W register. Some channels have an
additional fixed divider which is always applied to the signal.

Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Luc Michel <luc@lmichel.fr>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 32 insertions, 1 deletions

diff --git a/hw/misc/bcm2835_cprman.c b/hw/misc/bcm2835_cprman.c
index 12fa781..71c1d7b 100644
--- a/hw/misc/bcm2835_cprman.c
+++ b/hw/misc/bcm2835_cprman.c
@@ -134,9 +134,40 @@ static const TypeInfo cprman_pll_info = {
 
 /* PLL channel */
 
+static bool pll_channel_is_enabled(CprmanPllChannelState *channel)
+{
+    /*
+     * XXX I'm not sure of the purpose of the LOAD field. The Linux driver does
+     * not set it when enabling the channel, but does clear it when disabling
+     * it.
+     */
+    return !FIELD_EX32(*channel->reg_a2w_ctrl, A2W_PLLx_CHANNELy, DISABLE)
+        && !(*channel->reg_cm & channel->hold_mask);
+}
+
 static void pll_channel_update(CprmanPllChannelState *channel)
 {
-    clock_update(channel->out, 0);
+    uint64_t freq, div;
+
+    if (!pll_channel_is_enabled(channel)) {
+        clock_update(channel->out, 0);
+        return;
+    }
+
+    div = FIELD_EX32(*channel->reg_a2w_ctrl, A2W_PLLx_CHANNELy, DIV);
+
+    if (!div) {
+        /*
+         * It seems that when the divider value is 0, it is considered as
+         * being maximum by the hardware (see the Linux driver).
+         */
+        div = R_A2W_PLLx_CHANNELy_DIV_MASK;
+    }
+
+    /* Some channels have an additional fixed divider */
+    freq = clock_get_hz(channel->pll_in) / (div * channel->fixed_divider);
+
+    clock_update_hz(channel->out, freq);
 }
 
 /* Update a PLL and all its channels */