Do we also need to reset HW when execlist mode is enabled?

From: Zhi Wang <zhi.a.wang@intel.com>
To: "intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>
Cc: "Niu, Bing" <bing.niu@intel.com>
Subject: Do we also need to reset HW when execlist mode is enabled?
Date: Wed, 24 Jun 2015 05:41:08 +0800	[thread overview]
Message-ID: <5589D274.8010306@intel.com> (raw)

Hi Experts:
	Recently we found that when i915 module got unloaded, when we were
debugging some bugs in XenGT. It would not reset HW under execlist mode.
I'm not sure if this is an issue. But if we keep loading/unloading
module with the different submission mode, e.g. from execlist mode to
ring buffer mode via loading/unloading i915, this should be a corner
case.... Maybe you can provide some advice, or make sure if we need to
fix it. :)

If so, we can submit a patch. :)

Code:
void i915_gem_context_fini(struct drm_device *dev)
{
        struct drm_i915_private *dev_priv = dev->dev_private;
        struct intel_context *dctx = dev_priv->ring[RCS].default_context;
        int i;

        if (dctx->legacy_hw_ctx.rcs_state) {
                /* The only known way to stop the gpu from accessing the
hw context is
                 * to reset it. Do this as the very last operation to
avoid confusing
                 * other code, leading to spurious errors. */
                intel_gpu_reset(dev);  // <------------ Move this one to
the beginning of the function.

Thanks,
Zhi.
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