linux-kernel - Re: [Intel-gfx] [PATCH 1/2] drm/i915: Remove redundant reprobe in i915_drm

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Date:   Thu, 3 Nov 2016 16:02:53 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Lyude <lyude@...hat.com>
Cc:     intel-gfx@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [Intel-gfx] [PATCH 1/2] drm/i915: Remove redundant reprobe in
 i915_drm_resume

On Thu, Nov 03, 2016 at 11:42:37AM -0400, Lyude wrote:
> Weine's investigation on benchmarking the suspend/resume process pointed
> out a lot of the time in suspend/resume is being spent reprobing. While
> the reprobing process is a lengthy one for good reason, we don't need to
> hold up the entire suspend/resume process while we wait for it to
> finish. Luckily as it turns out, we already trigger a full connector
> reprobe in i915_hpd_poll_init_work(), so we can just ditch reprobing in
> i915_drm_resume() entirely.
> 
> This won't lead to less time spent resuming just yet since now the
> bottleneck will be waiting for the mode_config lock in
> drm_kms_helper_poll_enable(), since that will be held as long as
> i915_hpd_poll_init_work() is reprobing all of the connectors. But we'll
> address that in the next patch.
> 
> Signed-off-by: Lyude <lyude@...hat.com>
> Cc: David Weinehall <david.weinehall@...ux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index bfb2efd..532cc0f 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -1602,8 +1602,6 @@ static int i915_drm_resume(struct drm_device *dev)
>  	 * notifications.
>  	 * */
>  	intel_hpd_init(dev_priv);
> -	/* Config may have changed between suspend and resume */
> -	drm_helper_hpd_irq_event(dev);

The comment is still apt. This code is known to be broken since it
doesn't detect a change in monitors (e.g. a change in external connectors
from docking) between suspend and resend. We still have to send the uevent.

+	drm_kms_helper_hotplug_event(dev);

which also depends upon us actually reseting the connector->status to
unknown in drm_mode_config_reset(), Daniel!
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre