Re: [PATCH] drm/i915: Update state before setting watermarks.

[Ander Conselvan De Oliveira <conselvan2@gmail.com>]

On Wed, 2016-02-24 at 14:54 +0100, Maarten Lankhorst wrote:
> When intel_update_watermarks is called on skylake it inspects
> crtc->state, which should show as disabled. This wasn't the case,
> and this resulted in a divide-by-zero in
> skl_ddb_get_pipe_allocation_limits when intel_update_watermarks was called.

I think there's a "in hw state readout" missing somewhere in the commit message.
Even better if the commit message explained that the state was fixed up too
late, after the call to intel_update_watermarks() was already done. It would be
more informative than "should show as disabled".

> 
>  ------------[ cut here ]------------
>  WARNING: CPU: 1 PID: 295 at drivers/gpu/drm/i915/intel_pm.c:2834
> skl_update_pipe_wm+0x102/0x8c0 [i915]()
>  WARN_ON(!config->num_pipes_active)
>  Modules linked in: coretemp i915(+)
> xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>  CPU: 1 PID: 295 Comm: systemd-udevd Tainted: G     U  W       4.5.0-rc4
> -xxxxxx #25
>  Hardware name: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>   0000000000000000 ffff88003777f5a8 ffffffff813485c2 ffff88003777f5f0
>   ffffffffa0236240 ffff88003777f5e0 ffffffff81050fce ffff8800aa420000
>   ffff8800aba18000 ffff8800aba18000 ffff880037304c00 ffff8800aa420000
>  Call Trace:
>   [<ffffffff813485c2>] dump_stack+0x67/0x95
>   [<ffffffff81050fce>] warn_slowpath_common+0x9e/0xc0
>   [<ffffffff8105103c>] warn_slowpath_fmt+0x4c/0x50
>   [<ffffffff8106945e>] ? flush_work+0x8e/0x280
>   [<ffffffff810693d5>] ? flush_work+0x5/0x280
>   [<ffffffffa016add2>] skl_update_pipe_wm+0x102/0x8c0 [i915]
>   [<ffffffffa016b96f>] skl_update_wm+0xff/0x5f0 [i915]
>   [<ffffffff810928ee>] ? trace_hardirqs_on_caller+0x15e/0x1d0
>   [<ffffffff8109296d>] ? trace_hardirqs_on+0xd/0x10
>   [<ffffffffa016ce6e>] intel_update_watermarks+0x1e/0x30 [i915]
>   [<ffffffffa01d3ee2>] intel_crtc_disable_noatomic+0xd2/0x150 [i915]
>   [<ffffffffa01dd3d2>] intel_modeset_setup_hw_state+0xdd2/0xde0 [i915]
>   [<ffffffffa01dfd83>] intel_modeset_init+0x15a3/0x1950 [i915]
>   [<ffffffffa02160b6>] i915_driver_load+0x13c6/0x1720 [i915]
>   [<ffffffff81522160>] ? add_sysfs_fw_map_entry+0x9b/0x9b
>   [<ffffffffa00b15ef>] drm_dev_register+0x6f/0xb0 [drm]
>   [<ffffffffa00b3b3a>] drm_get_pci_dev+0x10a/0x1d0 [drm]
>   [<ffffffffa01582d9>] i915_pci_probe+0x49/0x50 [i915]
>   [<ffffffff8138ae30>] pci_device_probe+0x80/0xf0
>   [<ffffffff8143e2ac>] driver_probe_device+0x1bc/0x3d0
>   [<ffffffff8143e526>] __driver_attach+0x66/0x90
>   [<ffffffff8143e4c0>] ? driver_probe_device+0x3d0/0x3d0
>   [<ffffffff8143be3b>] bus_for_each_dev+0x5b/0xa0
>   [<ffffffff8143db3e>] driver_attach+0x1e/0x20
>   [<ffffffff8143d461>] bus_add_driver+0x151/0x270
>   [<ffffffff8143eabc>] driver_register+0x8c/0xd0
>   [<ffffffff8138a2ed>] __pci_register_driver+0x5d/0x60
>   [<ffffffffa00b3c58>] drm_pci_init+0x58/0xf0 [drm]
>   [<ffffffff8109296d>] ? trace_hardirqs_on+0xd/0x10
>   [<ffffffffa02aa000>] ? 0xffffffffa02aa000
>   [<ffffffffa02aa094>] i915_init+0x94/0x9b [i915]
>   [<ffffffff81000423>] do_one_initcall+0x113/0x1f0
>   [<ffffffff810a4b21>] ? rcu_read_lock_sched_held+0x61/0x90
>   [<ffffffff811601dc>] ? kmem_cache_alloc_trace+0x1cc/0x280
>   [<ffffffff8111110a>] do_init_module+0x60/0x1c8
>   [<ffffffff810c731b>] load_module+0x1ceb/0x2410
>   [<ffffffff810c3a60>] ? store_uevent+0x40/0x40
>   [<ffffffff811763d1>] ? kernel_read+0x41/0x60
>   [<ffffffff810c7c1d>] SYSC_finit_module+0x8d/0xa0
>   [<ffffffff810c7c4e>] SyS_finit_module+0xe/0x10
>   [<ffffffff815f1e97>] entry_SYSCALL_64_fastpath+0x12/0x6f
>  ---[ end trace 1149e9ab3695a423 ]---
>  ------------[ cut here ]------------
> 
> Reported-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
> diff --git a/drivers/gpu/drm/i915/intel_display.c
> b/drivers/gpu/drm/i915/intel_display.c
> index deee56010eee..d9e0470419a1 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -6358,6 +6358,7 @@ static void i9xx_crtc_disable(struct drm_crtc *crtc)
>  
>  static void intel_crtc_disable_noatomic(struct drm_crtc *crtc)
>  {
> +	struct intel_encoder *encoder;
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  	struct drm_i915_private *dev_priv = to_i915(crtc->dev);
>  	enum intel_display_power_domain domain;
> @@ -6378,6 +6379,19 @@ static void intel_crtc_disable_noatomic(struct drm_crtc
> *crtc)
>  	dev_priv->display.crtc_disable(crtc);
>  	intel_crtc->active = false;
>  	intel_fbc_disable(intel_crtc);

Would it make sense to do this before intel_fbc_disable() and ->crtc_disable()?
The bug here was a problem of calling into the lower layers with a bad state, so
I think it would be good to first take care of that before calling any other
functions.

With improved commit message, this is

Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>

Ander

> +
> +	DRM_DEBUG_KMS("[CRTC:%d] hw state adjusted, was enabled, now
> disabled\n",
> +		      crtc->base.id);
> +
> +	WARN_ON(drm_atomic_set_mode_for_crtc(crtc->state, NULL) < 0);
> +	crtc->state->active = false;
> +	crtc->enabled = false;
> +	crtc->state->connector_mask = 0;
> +	crtc->state->encoder_mask = 0;
> +
> +	for_each_encoder_on_crtc(crtc->dev, crtc, encoder)
> +		encoder->base.crtc = NULL;
> +
>  	intel_update_watermarks(crtc);
>  	intel_disable_shared_dpll(intel_crtc);
>  
> @@ -15526,38 +15540,9 @@ static void intel_sanitize_crtc(struct intel_crtc
> *crtc)
>  
>  	/* Adjust the state of the output pipe according to whether we
>  	 * have active connectors/encoders. */
> -	if (!intel_crtc_has_encoders(crtc))
> +	if (crtc->active && !intel_crtc_has_encoders(crtc))
>  		intel_crtc_disable_noatomic(&crtc->base);
>  
> -	if (crtc->active != crtc->base.state->active) {
> -		struct intel_encoder *encoder;
> -
> -		/* This can happen either due to bugs in the get_hw_state
> -		 * functions or because of calls to
> intel_crtc_disable_noatomic,
> -		 * or because the pipe is force-enabled due to the
> -		 * pipe A quirk. */
> -		DRM_DEBUG_KMS("[CRTC:%d] hw state adjusted, was %s, now
> %s\n",
> -			      crtc->base.base.id,
> -			      crtc->base.state->enable ? "enabled" :
> "disabled",
> -			      crtc->active ? "enabled" : "disabled");
> -
> -		WARN_ON(drm_atomic_set_mode_for_crtc(crtc->base.state, NULL)
> < 0);
> -		crtc->base.state->active = crtc->active;
> -		crtc->base.enabled = crtc->active;
> -		crtc->base.state->connector_mask = 0;
> -		crtc->base.state->encoder_mask = 0;
> -
> -		/* Because we only establish the connector -> encoder ->
> -		 * crtc links if something is active, this means the
> -		 * crtc is now deactivated. Break the links. connector
> -		 * -> encoder links are only establish when things are
> -		 *  actually up, hence no need to break them. */
> -		WARN_ON(crtc->active);
> -
> -		for_each_encoder_on_crtc(dev, &crtc->base, encoder)
> -			encoder->base.crtc = NULL;
> -	}
> -
>  	if (crtc->active || HAS_GMCH_DISPLAY(dev)) {
>  		/*
>  		 * We start out with underrun reporting disabled to avoid
> races.
> 
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