Re: [PATCH] drm/i915: limit PPGTT size to 2GB in 32-bit platforms

[Michel Thierry <michel.thierry@xxxxxxxxx>]

On 5/28/2015 4:39 PM, Chris Wilson wrote:

On Thu, May 28, 2015 at 04:24:47PM +0100, Michel Thierry wrote:

We already set this limit for the GGTT.

This is a temporary patch until a full replacement of size_t variables
(inadequate in 32-bit kernel) is in place.

Regression from:
	commit a4e0bedca678c81eea4cd79a4bd502335639f73a
	Author: Michel Thierry <michel.thierry@xxxxxxxxx>
	Date:   Wed Apr 8 12:13:35 2015 +0100

		drm/i915: Use complete address space in true PPGTT

Suggested-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
Signed-off-by: Michel Thierry <michel.thierry@xxxxxxxxx>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 17b7df0..ffecb87 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -951,7 +951,15 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 	gen8_initialize_pd(&ppgtt->base, ppgtt->scratch_pd);
 
 	ppgtt->base.start = 0;
+
+#ifdef CONFIG_X86_32
+	/* Limit 32b platforms to GGTT size (2GB) */

Forgot the comment about why the limit is inplace and when it can be
lifted. Remember comments are for *why* not *what*.

+	struct drm_i915_private *dev_priv = ppgtt->base.dev->dev_private;

Fancy new fangled C.

+	ppgtt->base.total = dev_priv->gtt.base.total;

	ppgtt->base.total = to_i915(ppgtt->base.dev)->gtt.base.total;

+#else
 	ppgtt->base.total = 1ULL << 32;
+#endif

Better yet would be:
	ppgtt->base.total = 1ULL << 32;
	if (IS_ENABLED(CONFIG_X86_32)) {
		/* While we have a proliferation of size_t variables
		 * we cannot represent the full ppgtt size on 32bit,
		 * so limit it to the same size as the GGTT (currently
		 * 2GiB).
		 */
		 ppgtt->base.total = to_i915(ppgtt->base.dev)->gtt.base.total;
	}

However, I am afraid that it will become obsolete but be forgotten to be
removed.

Yes, this is just for 4.2, Mika started working on a patch to replace the size_t variables.
I'll update this with your changes.

Thanks,

-Chris

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