Re: [PATCH] drm/i915: Fix irq enable tracking in driver load

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 27 Aug 2014, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> A bunch of warnings fire on some ->irq_postinstall hooks since those
> can enable interrupts (e.g. rps interrupts). And then our ordering
> self-checks fire and complain.
>
> To fix that set the tracking boolen before enabling the irqs witho
> drm_irq_install. Quoting the discussion with Jesse why that's safe:

Yi Sun's testing result needs to be addressed one way or another before
merging this:

http://mid.gmane.org/D9F66AA509623343B6A9A3D4502D5A52112B0676@SHSMSX101.ccr.corp.intel.com

BR,
Jani.


>
> On Tue, Aug 26, 2014 at 11:18 PM, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
>> Yes, it might work, but if you look through the history, we set this
>> field carefully; first to true in the irq_init code, then to false only
>> after the irq_install completes.  So I think your fragility arguments
>> apply to this change too.
>
> Well we've done it in 4 commits or so, but currently we have:
>
> - Set irqs_disabled to true early in driver load to make sure checks
> that. That's done in irq_init, which is totally not the function that
> enables interrupts, only the function that initializes all the vtables
> and similar things. We actually have a fairly sane naming scheme
> nowadays (not fully consistent ofc): _init is sw setup,
> _enable/_hw_init is the actual hw setup. That is done in
> 95f25beddba2ec9510b249740bacc11eca70cf75
>
> - Set irqs_disabled to false right after the irqs are actually
> enabled. This is done in ed2e6df18935beb3d63613c50103bf9757b2aa85
>
> So my change should only move the flag change over the ->preinstall
> and ->postinstall hooks. I've done a little audit and didn't spot
> anything amiss. Furthermore the runtime pm setup already clears
> irqs_disabled _before_ calling these two hooks.
>
> This regression has been introduced in
>
> commit ed2e6df18935beb3d63613c50103bf9757b2aa85
> Author: Jesse Barnes <jbarnes@virtuousgeek.org>
> Date:   Fri Jun 20 09:39:36 2014 -0700
>
>     drm/i915: clear pm._irqs_disabled field after installing IRQs
>
> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> Cc: Oliver Hartkopp <socketcan@hartkopp.net>
> Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_dma.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index 3b24e3bb2106..498980661b2f 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -1336,12 +1336,17 @@ static int i915_load_modeset_init(struct drm_device *dev)
>  
>  	intel_power_domains_init_hw(dev_priv);
>  
> +	/*
> +	 * We enable some interrupt sources in our postinstall hooks, so mark
> +	 * interrupts as enabled _before_ actually enabling them to avoid
> +	 * special cases in our ordering checks.
> +	 */
> +	dev_priv->pm._irqs_disabled = false;
> +
>  	ret = drm_irq_install(dev, dev->pdev->irq);
>  	if (ret)
>  		goto cleanup_gem_stolen;
>  
> -	dev_priv->pm._irqs_disabled = false;
> -
>  	/* Important: The output setup functions called by modeset_init need
>  	 * working irqs for e.g. gmbus and dp aux transfers. */
>  	intel_modeset_init(dev);
> -- 
> 2.0.1
>

-- 
Jani Nikula, Intel Open Source Technology Center