[v2,09/15] hw/misc/bcm2835_cprman: implement PLL channels behaviour

Commit Message

Luc Michel Oct. 5, 2020, 7:56 p.m. UTC

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 <[e-mail]>
Signed-off-by: Luc Michel <[e-mail]>
---
 hw/misc/bcm2835_cprman.c | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

Comments

Philippe Mathieu-Daudé Oct. 6, 2020, 9:07 a.m. UTC | #1

On 10/5/20 9:56 PM, Luc Michel wrote:
> 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 <[e-mail]>
> Signed-off-by: Luc Michel <[e-mail]>
> ---
>  hw/misc/bcm2835_cprman.c | 33 ++++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <[e-mail]>

Patch

diff --git a/hw/misc/bcm2835_cprman.c b/hw/misc/bcm2835_cprman.c
index 12fa78181b..71c1d7b9e7 100644
--- a/hw/misc/bcm2835_cprman.c
+++ b/hw/misc/bcm2835_cprman.c
@@ -132,13 +132,44 @@  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 */
 static void pll_update_all_channels(BCM2835CprmanState *s,
                                     CprmanPllState *pll)