On Thu, 18 Apr 2024 at 21:39, Raphael Poggi
<raphael.poggi@lynxleap.co.uk> wrote:
Hi Philippe,
Le jeu. 18 avr. 2024 à 20:43, Philippe Mathieu-Daudé
<philmd@linaro.org> a écrit :
Hi Raphael,
On 18/4/24 21:16, Raphael Poggi wrote:
When dealing with few clocks depending with each others, sometimes
we might only want to update the multiplier/diviser on a specific clock
(cf clockB in drawing below) and call "clock_propagate(clockA)" to
update the childs period according to the potential new multiplier/diviser
values.
+--------+ +--------+ +--------+
| clockA | --> | clockB | --> | clockC |
+--------+ +--------+ +--------+
The actual code would not allow that because, since we cannot call
"clock_propagate" directly on a child, it would exit on the
first child has the period has not changed for clockB, only clockC is
Typo "as the period has not changed"?
That's a typo indeed, thanks!
Why can't you call clock_propagate() on a child?
There is an assert "assert(clk->source == NULL);" in clock_propagate().
If I am not wrong, clk->source is set when the clock has a parent.
I think that assertion is probably there because we didn't
originally have the idea of a clock having a multiplier/divider
setting. So the idea was that calling clock_propagate() on a
clock with a parent would always be wrong, because the only
reason for its period to change would be if the parent had
changed, and if the parent changes then clock_propagate()
should be called on the parent.
We added mul/div later, and we (I) didn't think through all
the consequences. If you change the mul/div settings on
clockB in this example then you need to call clock_propagate()
on it, so we should remove that assert(). Then when you change
the mul/div on clockB you can directly clock_propagate(clockB),
and I don't think you need this patch at that point.