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

[Atwood, Matthew S]

intel_csr_load_program can fail (if not supported by SoC, or if file is size 0) and theres no conditional that it succeeds before releasing power_put on POWER_DOMAIN_INIT, enabling runtime PM. 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?
________________________________________
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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