Re: [PATCH v4 5/7] drm/panfrost: Add support for multiple power domains

[Saravana Kannan]

On Tue, Feb 11, 2020 at 5:58 PM Rob Herring <robh+dt@xxxxxxxxxx> wrote:
>
> On Tue, Feb 11, 2020 at 2:09 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
> >
> > On Tue, Feb 11, 2020 at 11:44 AM Rob Herring <robh+dt@xxxxxxxxxx> wrote:
> > >
> > > +Saravana
> > >
> > > On Thu, Feb 6, 2020 at 11:27 PM Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote:
> > > >
> > > > When there is a single power domain per device, the core will
> > > > ensure the power domain is switched on (so it is technically
> > > > equivalent to having not power domain specified at all).
> > > >
> > > > However, when there are multiple domains, as in MT8183 Bifrost
> > > > GPU, we need to handle them in driver code.
> > > >
> > > > Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
> > > >
> > > > ---
> > > >
> > > > The downstream driver we use on chromeos-4.19 currently uses 2
> > > > additional devices in device tree to accomodate for this [1], but
> > > > I believe this solution is cleaner.
> > > >
> > > > [1] https://chromium.googlesource.com/chromiumos/third_party/kernel/+/refs/heads/chromeos-4.19/drivers/gpu/arm/midgard/platform/mediatek/mali_kbase_runtime_pm.c#31
> > > >
> > > > v4:
> > > >  - Match the exact power domain names as specified in the compatible
> > > >    struct, instead of just matching the number of power domains.
> > > >    [Review: Ulf Hansson]
> > > >  - Dropped print and reordered function [Review: Steven Price]
> > > >  - nits: Run through latest version of checkpatch:
> > > >    - Use WARN instead of BUG_ON.
> > > >    - Drop braces for single expression if block.
> > > > v3:
> > > >  - Use the compatible matching data to specify the number of power
> > > >    domains. Note that setting 0 or 1 in num_pm_domains is equivalent
> > > >    as the core will handle these 2 cases in the exact same way
> > > >    (automatically, without driver intervention), and there should
> > > >    be no adverse consequence in this case (the concern is about
> > > >    switching on only some power domains and not others).
> > > >
> > > >  drivers/gpu/drm/panfrost/panfrost_device.c | 97 ++++++++++++++++++++--
> > > >  drivers/gpu/drm/panfrost/panfrost_device.h | 11 +++
> > > >  drivers/gpu/drm/panfrost/panfrost_drv.c    |  2 +
> > > >  3 files changed, 102 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> > > > index 3720d50f6d9f965..8136babd3ba9935 100644
> > > > --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> > > > +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> > > > @@ -5,6 +5,7 @@
> > > >  #include <linux/clk.h>
> > > >  #include <linux/reset.h>
> > > >  #include <linux/platform_device.h>
> > > > +#include <linux/pm_domain.h>
> > > >  #include <linux/regulator/consumer.h>
> > > >
> > > >  #include "panfrost_device.h"
> > > > @@ -120,6 +121,79 @@ static void panfrost_regulator_fini(struct panfrost_device *pfdev)
> > > >                         pfdev->regulators);
> > > >  }
> > > >
> > > > +static void panfrost_pm_domain_fini(struct panfrost_device *pfdev)
> > > > +{
> > > > +       int i;
> > > > +
> > > > +       for (i = 0; i < ARRAY_SIZE(pfdev->pm_domain_devs); i++) {
> > > > +               if (!pfdev->pm_domain_devs[i])
> > > > +                       break;
> > > > +
> > > > +               if (pfdev->pm_domain_links[i])
> > > > +                       device_link_del(pfdev->pm_domain_links[i]);
> > > > +
> > > > +               dev_pm_domain_detach(pfdev->pm_domain_devs[i], true);
> > > > +       }
> > > > +}
> > > > +
> > > > +static int panfrost_pm_domain_init(struct panfrost_device *pfdev)
> > > > +{
> > > > +       int err;
> > > > +       int i, num_domains;
> > > > +
> > > > +       num_domains = of_count_phandle_with_args(pfdev->dev->of_node,
> > > > +                                                "power-domains",
> > > > +                                                "#power-domain-cells");
> > > > +
> > > > +       /*
> > > > +        * Single domain is handled by the core, and, if only a single power
> > > > +        * the power domain is requested, the property is optional.
> > > > +        */
> > > > +       if (num_domains < 2 && pfdev->comp->num_pm_domains < 2)
> > > > +               return 0;
> > > > +
> > > > +       if (num_domains != pfdev->comp->num_pm_domains) {
> > > > +               dev_err(pfdev->dev,
> > > > +                       "Incorrect number of power domains: %d provided, %d needed\n",
> > > > +                       num_domains, pfdev->comp->num_pm_domains);
> > > > +               return -EINVAL;
> > > > +       }
> > > > +
> > > > +       if (WARN(num_domains > ARRAY_SIZE(pfdev->pm_domain_devs),
> > > > +                       "Too many supplies in compatible structure.\n"))
> > > > +               return -EINVAL;
> > > > +
> > > > +       for (i = 0; i < num_domains; i++) {
> > > > +               pfdev->pm_domain_devs[i] =
> > > > +                       dev_pm_domain_attach_by_name(pfdev->dev,
> > > > +                                       pfdev->comp->pm_domain_names[i]);
> > > > +               if (IS_ERR_OR_NULL(pfdev->pm_domain_devs[i])) {
> > > > +                       err = PTR_ERR(pfdev->pm_domain_devs[i]) ? : -ENODATA;
> > > > +                       pfdev->pm_domain_devs[i] = NULL;
> > > > +                       dev_err(pfdev->dev,
> > > > +                               "failed to get pm-domain %s(%d): %d\n",
> > > > +                               pfdev->comp->pm_domain_names[i], i, err);
> > > > +                       goto err;
> > > > +               }
> > > > +
> > > > +               pfdev->pm_domain_links[i] = device_link_add(pfdev->dev,
> > > > +                               pfdev->pm_domain_devs[i], DL_FLAG_PM_RUNTIME |
> > > > +                               DL_FLAG_STATELESS | DL_FLAG_RPM_ACTIVE);
> > >
> > > We're in the process of adding device links based on DT properties.
> > > Shouldn't we add power domains to that? See drivers/of/property.c for
> > > what's handled.
> >
> > Rob,
> >
> > drivers/of/property.c doesn't enable the RPM_ACTIVE AND PM_RUNTIME
> > flags. Wanted to start off conservative.
>
> I worry that you can't add it later without potentially breaking platforms.
>
> I haven't checked, but I assume these flags make runtime PM honor
> device links? That seems like the more conservative option (more
> reasons why a device can't suspend).

Conservative as in, if of_devlink adds the RPM_ACTIVE flag, the
drivers can't remove it.

> > But adding command line ops
> > to change the default flags shouldn't be difficult. But before I do
> > that, I want to change of_devlink to
> > fw_devlink=<disabled|permissive|enabled>. May be I can extend that to
> > "disabled, permissive, suspend, runtime".
>
> I think any command line option should be debug primarily. It's kind
> of a big hammer.

It is a big hammer. But it's better than disabling of_devlink
altogether. There is always going to be weird hardware that won't work
with of_devlink if all the device link flags are set. They'll need
some fix up of drivers and/or clean up of DT. And having different
of_devlink command line options would at least let those hardware to
run with as much of_devlink enabled as possible while working to get
more fixes into the kernel. That way, we can make sure we don't
regress further while trying to improve the support.

> Can drivers adjust the flags themselves? Just modify the flags rather
> than trying to create new links?

They can, but only in an additive manner. And the way to do it would
be to add a device link like usual and the framework takes care of
combining the flags. That's why I don't set most of the flags by
default.


-Saravana