Re: [PATCH v10 5/8] soc/tegra: pmc: Implement dev_get_performance_state() callback

Viresh Kumar
2021-09-01T07:17:01Z

On 01-09-21, 09:57, Dmitry Osipenko wrote:
> 01.09.2021 09:10, Viresh Kumar пишет:
> > So you create the OPP table and just after that you remove it ? Just
> > to get the current OPP and pstate ? This doesn't look okay.
> >
> > Moreover, this routine must be implemented with the expectation that
> > the genpd core can call it anytime it wants, not just at the
> > beginning. And so if the table is already setup by someone else then,
> > then this all will just fail.
>
> This is not doable using the current OPP API, it doesn't allow to
> re-use initialized OPP table.

That isn't correct, you can call dev_pm_opp_of_add_table() as many
times as you want. It will just increase the refcount and return the
next time.

Yes, you can call the APIs like set-clk-name or supported-hw, since
they are supposed to be set only once.

> The current limitation is okay because genpd core doesn't call
> routine anytime.

Yeah, but is broken by design. People can make changes to genpd core
later on to call it as many times and they aren't required to have a
look at all the users to see who abused the API and who didn't.

> > Can you give the sequence in which the whole thing works out with
> > respect to the OPP core? who calls
> > devm_tegra_core_dev_init_opp_table() and when, and when exactly will
> > this routine get called, etc ?
> >
>
> gr3d_probe(struct platform_device *pdev)

Thanks for this.

> {
> gr3d_init_power(dev)
> {
> static const char * const opp_genpd_names[] = { "3d0", "3d1", NULL };
>
> devm_pm_opp_attach_genpd(dev, opp_genpd_names)
> {
> dev_pm_opp_attach_genpd(dev, names, virt_devs)
> {
> // takes and holds table reference
> opp_table = _add_opp_table(dev, false);
>
> while (*name) {
> // first attachment succeeds,
> // second fails with "tegra-gr3d 54180000.gr3d: failed to set OPP clk: -EBUSY"
> dev_pm_domain_attach_by_name(dev, *name)
> {
> tegra_pmc_pd_dev_get_performance_state(dev)
> {
> dev_pm_opp_set_clkname(dev, NULL);
> dev_pm_opp_of_add_table(dev);

What you end up doing here is pretty much like
devm_tegra_core_dev_init_opp_table_simple(), right ?

> opp = dev_pm_opp_get_current(dev);
> dev_pm_opp_of_remove_table(dev);
> dev_pm_opp_put_clkname(opp_table);

You shouldn't be required to do this at all.

> ...
> }
> // opp_table->clk = ERR_PTR(-EINVAL) after the first attachment
> }
> }
> }
> }
> }
>
> devm_tegra_core_dev_init_opp_table_simple(&pdev->dev);

Can we make the call at the beginning ? before calling
gr3d_init_power() ? I mean you should only be required to initialize
the OPP table just once.

If not, then what about calling
devm_tegra_core_dev_init_opp_table_simple() from here and from
tegra_pmc_pd_dev_get_performance_state() as well ?

And update devm_tegra_core_dev_init_opp_table_simple() to call
dev_pm_opp_get_opp_table() first and return early if the OPP table is
already initialized ?

--
viresh