[Intel-gfx] [PATCH] drm/i915: decouple runtime PM enablement from DMC presence

[Imre Deak]

On Wed, Jun 14, 2017 at 08:40:55PM +0300, Atwood, Matthew S wrote:
> intel_csr_load_program can fail (if not supported by SoC, or if file
> is size 0)

Those are really just sanity checks, they can't happen normally. We
should actually convert them to be WARNs.

> and theres no conditional that it succeeds before releasing
> power_put on POWER_DOMAIN_INIT, enabling runtime PM.

It can't fail during loading, HAS_CSR() is already checked in
intel_csr_ucode_init() and dev_priv->csr.dmc_payload is checked right
before calling intel_csr_load_program().

> As long as the driver *thinks* it has a valid path to a DMC firmware
> this will execute.
> 
> "without DMC loaded we want to keep runtime PM disabled" - Why?

There is no reason to support that configuration.

> ________________________________________
> From: Deak, Imre
> Sent: Wednesday, June 14, 2017 10:33 AM
> To: Atwood, Matthew S
> Cc: intel-gfx at lists.freedesktop.org; marcheu at google.com; Matt Atwood
> Subject: Re: [Intel-gfx] [PATCH] drm/i915: decouple runtime PM enablement from DMC presence
> 
> On Wed, Jun 14, 2017 at 10:12:21AM -0700, matthew.s.atwood at intel.com wrote:
> > From: Matt Atwood <matthew.s.atwood at intel.corp-partner.google.com>
> >
> > Runtime PM is disabled when DMC firmware is not present. Runtime PM is still
> > enabled even if DMC firmware fails to load.
> 
> Hm, that would be a bug, but I can't see how it can happen; could you
> explain? We get a runtime PM reference in intel_csr_ucode_init() and
> only put it if we loaded the firmware successfully.
> 
> > This patch enables runtime PM to be enabled if DMC firmware is not present.
> 
> Without DMC loaded we want to keep runtime PM disabled.
> 
> --Imre
> 
> >
> > Signed-off-by: Matt Atwood <matthew.s.atwood at intel.corp-partner.google.com>
> > ---
> >  drivers/gpu/drm/i915/intel_csr.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_csr.c b/drivers/gpu/drm/i915/intel_csr.c
> > index 965988f..3e4e705 100644
> > --- a/drivers/gpu/drm/i915/intel_csr.c
> > +++ b/drivers/gpu/drm/i915/intel_csr.c
> > @@ -411,8 +411,6 @@ static void csr_load_work_fn(struct work_struct *work)
> >       if (dev_priv->csr.dmc_payload) {
> >               intel_csr_load_program(dev_priv);
> >
> > -             intel_display_power_put(dev_priv, POWER_DOMAIN_INIT);
> > -
> >               DRM_INFO("Finished loading DMC firmware %s (v%u.%u)\n",
> >                        dev_priv->csr.fw_path,
> >                        CSR_VERSION_MAJOR(csr->version),
> > @@ -420,10 +418,11 @@ static void csr_load_work_fn(struct work_struct *work)
> >       } else {
> >               dev_notice(dev_priv->drm.dev,
> >                          "Failed to load DMC firmware"
> > -                        " [" FIRMWARE_URL "],"
> > -                        " disabling runtime power management.\n");
> > +                        " [" FIRMWARE_URL "]");
> >       }
> >
> > +     intel_display_power_put(dev_priv, POWER_DOMAIN_INIT);
> > +
> >       release_firmware(fw);
> >  }
> >
> > --
> > 2.7.4
> >
> > _______________________________________________
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> > Intel-gfx at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>