TTM placement & caching issue/questions

[Jerome Glisse]

On Thu, Sep 04, 2014 at 12:25:23PM +1000, Benjamin Herrenschmidt wrote:
> On Wed, 2014-09-03 at 22:07 -0400, Jerome Glisse wrote:
> 
> > So in the meantime the attached patch should work, it just silently ignore
> > the caching attribute request on non x86 instead of pretending that things
> > are setup as expected and then latter the radeon ou nouveau hw unsetting
> > the snoop bit.
> > 
> > It's not tested but i think it should work.
> 
> I'm still getting placements with !CACHED going from bo_memcpy in
> ttm_io_prot() though ... I'm looking at filtering the placement
> attributes instead.
> 
> Ben.

Ok so this one should do the trick.


> 
> > > 
> > > Cheers,
> > > Jérôme
> > > 
> > > > 
> > > > Cheers,
> > > > Ben.
> > > > 
> > > > 
> > > > _______________________________________________
> > > > dri-devel mailing list
> > > > dri-devel at lists.freedesktop.org
> > > > http://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
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>From def7a056d042220f91016d0a7c245ba8e96f90ba Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= <jglisse at redhat.com>
Date: Wed, 3 Sep 2014 22:04:34 -0400
Subject: [PATCH] drm/ttm: force cached mapping on non x86 platform.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

People interested in providing uncached or write combined mapping
on there architecture need to do the ground work inside there arch
specific code to allow to break the linear kernel mapping so that
page mapping attributes can be updated, in the meantime force cached
mapping for non x86 architecture.

Signed-off-by: Jérôme Glisse <jglisse at redhat.com>
---
 drivers/gpu/drm/radeon/radeon_ttm.c |  2 +-
 drivers/gpu/drm/ttm/ttm_bo.c        |  2 +-
 drivers/gpu/drm/ttm/ttm_tt.c        | 47 ++++++++++++++++++++++++++++---------
 include/drm/ttm/ttm_bo_driver.h     |  2 +-
 4 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
index 72afe82..4dd5060 100644
--- a/drivers/gpu/drm/radeon/radeon_ttm.c
+++ b/drivers/gpu/drm/radeon/radeon_ttm.c
@@ -304,7 +304,7 @@ static int radeon_move_vram_ram(struct ttm_buffer_object *bo,
 		return r;
 	}
 
-	r = ttm_tt_set_placement_caching(bo->ttm, tmp_mem.placement);
+	r = ttm_tt_set_placement_caching(bo->ttm, &tmp_mem.placement);
 	if (unlikely(r)) {
 		goto out_cleanup;
 	}
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 3da89d5..4dc21c3 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -305,7 +305,7 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
 				goto out_err;
 		}
 
-		ret = ttm_tt_set_placement_caching(bo->ttm, mem->placement);
+		ret = ttm_tt_set_placement_caching(bo->ttm, &mem->placement);
 		if (ret)
 			goto out_err;
 
diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index bf080ab..7cbdb48 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -89,14 +89,6 @@ static inline int ttm_tt_set_page_caching(struct page *p,
 
 	return ret;
 }
-#else /* CONFIG_X86 */
-static inline int ttm_tt_set_page_caching(struct page *p,
-					  enum ttm_caching_state c_old,
-					  enum ttm_caching_state c_new)
-{
-	return 0;
-}
-#endif /* CONFIG_X86 */
 
 /*
  * Change caching policy for the linear kernel map
@@ -149,19 +141,52 @@ out_err:
 	return ret;
 }
 
-int ttm_tt_set_placement_caching(struct ttm_tt *ttm, uint32_t placement)
+int ttm_tt_set_placement_caching(struct ttm_tt *ttm, uint32_t *placement)
 {
 	enum ttm_caching_state state;
 
-	if (placement & TTM_PL_FLAG_WC)
+	if (*placement & TTM_PL_FLAG_WC)
 		state = tt_wc;
-	else if (placement & TTM_PL_FLAG_UNCACHED)
+	else if (*placement & TTM_PL_FLAG_UNCACHED)
 		state = tt_uncached;
 	else
 		state = tt_cached;
 
 	return ttm_tt_set_caching(ttm, state);
 }
+#else /* CONFIG_X86 */
+int ttm_tt_set_placement_caching(struct ttm_tt *ttm, uint32_t *placement)
+{
+	if (placement & (TTM_PL_TT | TTM_PL_FLAG_SYSTEM)) {
+		ttm->caching_state = tt_cached;
+	} else {
+		if (placement & TTM_PL_FLAG_WC)
+			ttm->caching_state = tt_wc;
+		else if (placement & TTM_PL_FLAG_UNCACHED)
+			ttm->caching_state = tt_uncached;
+		else
+			ttm->caching_state = tt_cached;
+	}
+	/*
+	 * Some architecture force cached so we need to reflect the
+	 * new ttm->caching_state into the mem->placement flags.
+	 */
+	*placement &= ~TTM_PL_MASK_CACHING;
+	switch (bo->ttm->caching_state) {
+	case tt_wc:
+		*placement |= TTM_PL_FLAG_WC;
+		break;
+	case tt_uncached:
+		*placement |= TTM_PL_FLAG_UNCACHED;
+		break;
+	case tt_cached:
+	default:
+		*placement |= TTM_PL_FLAG_CACHED;
+		break;
+	}
+	return 0;
+}
+#endif /* CONFIG_X86 */
 EXPORT_SYMBOL(ttm_tt_set_placement_caching);
 
 void ttm_tt_destroy(struct ttm_tt *ttm)
diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
index 1d9f0f1..cbc5ad2 100644
--- a/include/drm/ttm/ttm_bo_driver.h
+++ b/include/drm/ttm/ttm_bo_driver.h
@@ -669,7 +669,7 @@ extern int ttm_tt_swapin(struct ttm_tt *ttm);
  * hit RAM. This function may be very costly as it involves global TLB
  * and cache flushes and potential page splitting / combining.
  */
-extern int ttm_tt_set_placement_caching(struct ttm_tt *ttm, uint32_t placement);
+extern int ttm_tt_set_placement_caching(struct ttm_tt *ttm, uint32_t *placement);
 extern int ttm_tt_swapout(struct ttm_tt *ttm,
 			  struct file *persistent_swap_storage);
 
-- 
1.9.3