Re: [PATCH v2 2/4] drm/i915: Fix system resume if PCI device remained enabled

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Apr 18, 2016 at 02:45:54PM +0300, Imre Deak wrote:
> During system resume we depended on pci_enable_device() also putting the
> device into PCI D0 state. This won't work if the PCI device was already
> enabled but still in D3 state. This is because pci_enable_device() is
> refcounted and will not change the HW state if called with a non-zero
> refcount. Leaving the device in D3 will make all subsequent device
> accesses fail.
> 
> This didn't cause a problem most of the time, since we resumed with an
> enable refcount of 0. But it fails at least after module reload because
> after that we also happen to leak a PCI device enable reference: During
> probing we call drm_get_pci_dev() which will enable the PCI device, but
> during device removal drm_put_dev() won't disable it. This is a bug of
> its own in DRM core, but without much harm as it only leaves the PCI
> device enabled. Fixing it is also a bit more involved, due to DRM
> mid-layering and because it affects non-i915 drivers too. The fix in
> this patch is valid regardless of the problem in DRM core.
> 
> v2:
> - Add a code comment about the relation of this fix to the freeze/thaw
>   vs. the suspend/resume phases. (Ville)
> - Add a code comment about the inconsistent ordering of set power state
>   and device enable calls. (Chris)
> 
> CC: Ville Syrjälä <ville.syrjala@linux.intel.com>
> CC: Chris Wilson <chris@chris-wilson.co.uk>
> CC: stable@vger.kernel.org
> Signed-off-by: Imre Deak <imre.deak@intel.com>

The PCI PM code is a bit of a mess, but it would be appear this should
do what we need.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/i915_drv.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index d550ae2..3b79e97 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -803,7 +803,7 @@ static int i915_drm_resume(struct drm_device *dev)
>  static int i915_drm_resume_early(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> -	int ret = 0;
> +	int ret;
>  
>  	/*
>  	 * We have a resume ordering issue with the snd-hda driver also
> @@ -814,6 +814,36 @@ static int i915_drm_resume_early(struct drm_device *dev)
>  	 * FIXME: This should be solved with a special hdmi sink device or
>  	 * similar so that power domains can be employed.
>  	 */
> +
> +	/*
> +	 * Note that we need to set the power state explicitly, since we
> +	 * powered off the device during freeze and the PCI core won't power
> +	 * it back up for us during thaw. Powering off the device during
> +	 * freeze is not a hard requirement though, and during the
> +	 * suspend/resume phases the PCI core makes sure we get here with the
> +	 * device powered on. So in case we change our freeze logic and keep
> +	 * the device powered we can also remove the following set power state
> +	 * call.
> +	 */
> +	ret = pci_set_power_state(dev->pdev, PCI_D0);
> +	if (ret) {
> +		DRM_ERROR("failed to set PCI D0 power state (%d)\n", ret);
> +		goto out;
> +	}
> +
> +	/*
> +	 * Note that pci_enable_device() first enables any parent bridge
> +	 * device and only then sets the power state for this device. The
> +	 * bridge enabling is a nop though, since bridge devices are resumed
> +	 * first. The order of enabling power and enabling the device is
> +	 * imposed by the PCI core as described above, so here we preserve the
> +	 * same order for the freeze/thaw phases.
> +	 *
> +	 * TODO: eventually we should remove pci_disable_device() /
> +	 * pci_enable_enable_device() from suspend/resume. Due to how they
> +	 * depend on the device enable refcount we can't anyway depend on them
> +	 * disabling/enabling the device.
> +	 */
>  	if (pci_enable_device(dev->pdev)) {
>  		ret = -EIO;
>  		goto out;
> -- 
> 2.5.0

-- 
Ville Syrjälä
Intel OTC