On 8/12/21 11:33 AM, Peter Maydell wrote:
> It is quite common for a clock tree to involve possibly programmable
> clock multipliers or dividers, where the frequency of a clock is for
> instance divided by 8 to produce a slower clock to feed to a
> particular device.
>
> Currently we provide no convenient mechanism for modelling this. You
> can implement it by having an input Clock and an output Clock, and
> manually setting the period of the output clock in the period-changed
> callback of the input clock, but that's quite clunky.
>
> This patch adds support in the Clock objects themselves for setting a
> multiplier or divider. The effect of setting this on a clock is that
> when the clock's period is changed, all the children of the clock are
> set to period * multiplier / divider, rather than being set to the
> same period as the parent clock.
This is super nice!
> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
> ---
> docs/devel/clocks.rst | 23 +++++++++++++++++++++++
> include/hw/clock.h | 29 +++++++++++++++++++++++++++++
> hw/core/clock-vmstate.c | 24 +++++++++++++++++++++++-
> hw/core/clock.c | 29 +++++++++++++++++++++++++----
> 4 files changed, 100 insertions(+), 5 deletions(-)
> +void clock_set_mul_div(Clock *clk, uint32_t multiplier, uint32_t divider)
> +{
> + assert(divider != 0);
I only wonder if we shouldn't check clock_is_enabled() here.
Maybe not assert, but at least report a GUEST_ERROR?
Also a trace-event "mul: %u -> %u, div: %u -> %u" would be useful IMHO.
> + clk->multiplier = multiplier;
> + clk->divider = divider;
> +}
