Re: [PATCH] interconnect: Skip call into provider if initial bw is zero

[Bryan O'Donoghue]

On 14/01/2023 01:24, Bryan O'Donoghue wrote:
> On 13/01/2023 22:07, Vivek Aknurwar wrote:
> > Currently framework sets bw even when init bw requirements are zero 
> > during
> > provider registration, thus resulting bulk of set bw to hw.
> > Avoid this behaviour by skipping provider set bw calls if init bw is 
> > zero.
> >
> > Signed-off-by: Vivek Aknurwar <quic_viveka@xxxxxxxxxxx>
> > ---
> >   drivers/interconnect/core.c | 17 ++++++++++-------
> >   1 file changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> > index 25debde..43ed595 100644
> > --- a/drivers/interconnect/core.c
> > +++ b/drivers/interconnect/core.c
> > @@ -977,14 +977,17 @@ void icc_node_add(struct icc_node *node, struct 
> > icc_provider *provider)
> >       node->avg_bw = node->init_avg;
> >       node->peak_bw = node->init_peak;
> > -    if (provider->pre_aggregate)
> > -        provider->pre_aggregate(node);
> > -
> > -    if (provider->aggregate)
> > -        provider->aggregate(node, 0, node->init_avg, node->init_peak,
> > -                    &node->avg_bw, &node->peak_bw);
> > +    if (node->avg_bw || node->peak_bw) {
> > +        if (provider->pre_aggregate)
> > +            provider->pre_aggregate(node);
> > +
> > +        if (provider->aggregate)
> > +            provider->aggregate(node, 0, node->init_avg, 
> > node->init_peak,
> > +                        &node->avg_bw, &node->peak_bw);
> > +        if (provider->set)
> > +            provider->set(node, node);
> > +    }
> > -    provider->set(node, node);
> >       node->avg_bw = 0;
> >       node->peak_bw = 0;
>
> I have the same comment/question for this patch that I had for the qcom 
> arch specific version of it. This patch seems to be doing at a higher 
> level what the patch below was doing at a lower level.
>
> https://lore.kernel.org/lkml/1039a507-c4cd-e92f-dc29-1e2169ce5078@xxxxxxxxxx/T/#m0c90588d0d1e2ab88c39be8f5f3a8f0b61396349
>
> what happens to earlier silicon - qcom silicon which previously made 
> explicit zero requests ?
>
> https://lore.kernel.org/lkml/1039a507-c4cd-e92f-dc29-1e2169ce5078@xxxxxxxxxx/T/#m589e8280de470e038249bb362634221771d845dd
>
> https://lkml.org/lkml/2023/1/3/1232
>
> Isn't it a better idea to let lower layer drivers differentiate what 
> they do ?
>
> For example on pre 5.4 qcom kernel silicon we might choose to set the 
> value to zero "because that's what the reference code did" but on newer 
> silicon we might opt to skip the zero configuration ?
>
> I'm happy to be shown the error of my ways but, absent testing to *show* 
> it doesn't impact existing legacy silicon, I think we should be wary of 
> this change.
>
> ---
> bod

Oh, and what is the effect on Samsung and i.MX silicon interconnect 
providers of skipping the zero set ?

---
bod