Re: [Qemu-devel] [PATCH v3 00/10] Clock framework API.

[KONRAD Frederic]

Le 06/23/2017 à 03:58 PM, Peter Maydell a écrit :
> On 23 June 2017 at 14:07, KONRAD Frederic <address@hidden> wrote:
> > Le 06/23/2017 à 02:47 PM, Peter Maydell a écrit :
> > > Each device "owns" its output clock objects, but input
> > > clocks are just pointers to the clock object owned by the
> > > device at the other end. In the board you wire up CI1 to C1,
> > > and CI2 to C2 (using link properties I guess).
> > > Then in device C you can implement the clock switching by
> > > some kind of bind(s->CI1, &s->C3) call because you have
> > > pointers to all the relevant clock objects.
> > >
> > > As I understand it your current implementation makes not
> > > just the output clocks C1 C2 C2 be clock objects, but also
> > > the inputs CI1 CI2, so effectively each link from a clock
> > > source to a clock sink has two objects involved.
>
> > Yes that makes sense but you won't have the name.
>
> I don't think that's a big deal.
>
> > And one other thing I wanted to have is beeing able to refresh
> > the clock tree without refreshing everything. If you start a
> > refresh from the "pointer" and it is bind to other things you
> > will refresh the other devices as well. Maybe we don't care or we
> > can workaround that but..
>
> The pointer is for your clock inputs -- when would you
> want to start a refresh from that? I would expect
> refreshes to only ever go downstream -- you update
> the config of your clock outputs and things downstream
> of them will update in turn.

I started with the goal in mind that the binding + the callback
can refresh themself without user intervention.

So actually the user only have to change the binding in case of a
clock selector.. Everything else is done by the framework.

For example if we want to change a multiplier through a register:

void register_write(..)
{
  /* Refresh related clock input. */
}

void clock_cb(..)
{
  return register_value * rate_in;
}

If we drop the clock first possibility:

void register_write(..)
{
  /* refresh all depending clock with
   * rate_in * register value.
   * Either this can be tricky as we need to know exactly which
   * clock need to be refreshed or we need to refresh everybody.
   * On the device example in the patch-set this can become a
   * mess.
   */
}

void clock_cb(..)
{
  return register_value * rate_in;
}

Second possibility:

void register_write(..)
{
  /* refresh the clock which is referenced as input.
   * This is easy BUT it will refresh all other devices bound to
   * this clock.
   */
}

void clock_cb(..)
{
  return register_value * rate_in;
}

Thanks,
Fred

> thanks
> -- PMM