drm/i915: Replace the array of pages with a scatterlist

Rather than have multiple data structures for describing our page layout
in conjunction with the array of pages, we can migrate all users over to
a scatterlist.

One major advantage, other than unifying the page tracking structures,
this offers is that we replace the vmalloc'ed array (which can be up to
a megabyte in size) with a chain of individual pages which helps reduce
memory pressure.

The disadvantage is that we then do not have a simple array to iterate,
or to access randomly. The common case for this is in the relocation
processing, which will typically fit within a single scatterlist page
and so be almost the same cost as the simple array. For iterating over
the array, the extra function call could be optimised away, but in
reality is an insignificant cost of either binding the pages, or
performing the pwrite/pread.

v2: Fix drm_clflush_sg() to not invoke wbinvd as well! And fix the
trivial compile error from rebasing.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 22 insertions, 29 deletions

diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
index 58e32f7c322..7fa655ac24d 100644
--- a/drivers/char/agp/intel-gtt.c
+++ b/drivers/char/agp/intel-gtt.c
@@ -84,40 +84,33 @@ static struct _intel_private {
 #define IS_IRONLAKE     intel_private.driver->is_ironlake
 #define HAS_PGTBL_EN    intel_private.driver->has_pgtbl_enable
 
-int intel_gtt_map_memory(struct page **pages, unsigned int num_entries,
-                         struct scatterlist **sg_list, int *num_sg)
+static int intel_gtt_map_memory(struct page **pages,
+                                unsigned int num_entries,
+                                struct sg_table *st)
 {
-        struct sg_table st;
         struct scatterlist *sg;
         int i;
 
-        if (*sg_list)
-                return 0; /* already mapped (for e.g. resume */
-
         DBG("try mapping %lu pages\n", (unsigned long)num_entries);
 
-        if (sg_alloc_table(&st, num_entries, GFP_KERNEL))
+        if (sg_alloc_table(st, num_entries, GFP_KERNEL))
                 goto err;
 
-        *sg_list = sg = st.sgl;
-
-        for (i = 0 ; i < num_entries; i++, sg = sg_next(sg))
+        for_each_sg(st->sgl, sg, num_entries, i)
                 sg_set_page(sg, pages[i], PAGE_SIZE, 0);
 
-        *num_sg = pci_map_sg(intel_private.pcidev, *sg_list,
-                                 num_entries, PCI_DMA_BIDIRECTIONAL);
-        if (unlikely(!*num_sg))
+        if (!pci_map_sg(intel_private.pcidev,
+                        st->sgl, st->nents, PCI_DMA_BIDIRECTIONAL))
                 goto err;
 
         return 0;
 
 err:
-        sg_free_table(&st);
+        sg_free_table(st);
         return -ENOMEM;
 }
-EXPORT_SYMBOL(intel_gtt_map_memory);
 
-void intel_gtt_unmap_memory(struct scatterlist *sg_list, int num_sg)
+static void intel_gtt_unmap_memory(struct scatterlist *sg_list, int num_sg)
 {
         struct sg_table st;
         DBG("try unmapping %lu pages\n", (unsigned long)mem->page_count);
@@ -130,7 +123,6 @@ void intel_gtt_unmap_memory(struct scatterlist *sg_list, int num_sg)
 
         sg_free_table(&st);
 }
-EXPORT_SYMBOL(intel_gtt_unmap_memory);
 
 static void intel_fake_agp_enable(struct agp_bridge_data *bridge, u32 mode)
 {
@@ -879,8 +871,7 @@ static bool i830_check_flags(unsigned int flags)
         return false;
 }
 
-void intel_gtt_insert_sg_entries(struct scatterlist *sg_list,
-                                 unsigned int sg_len,
+void intel_gtt_insert_sg_entries(struct sg_table *st,
                                  unsigned int pg_start,
                                  unsigned int flags)
 {
@@ -892,12 +883,11 @@ void intel_gtt_insert_sg_entries(struct scatterlist *sg_list,
 
         /* sg may merge pages, but we have to separate
          * per-page addr for GTT */
-        for_each_sg(sg_list, sg, sg_len, i) {
+        for_each_sg(st->sgl, sg, st->nents, i) {
                 len = sg_dma_len(sg) >> PAGE_SHIFT;
                 for (m = 0; m < len; m++) {
                         dma_addr_t addr = sg_dma_address(sg) + (m << PAGE_SHIFT);
-                        intel_private.driver->write_entry(addr,
-                                                          j, flags);
+                        intel_private.driver->write_entry(addr, j, flags);
                         j++;
                 }
         }
@@ -905,8 +895,10 @@ void intel_gtt_insert_sg_entries(struct scatterlist *sg_list,
 }
 EXPORT_SYMBOL(intel_gtt_insert_sg_entries);
 
-void intel_gtt_insert_pages(unsigned int first_entry, unsigned int num_entries,
-                            struct page **pages, unsigned int flags)
+static void intel_gtt_insert_pages(unsigned int first_entry,
+                                   unsigned int num_entries,
+                                   struct page **pages,
+                                   unsigned int flags)
 {
         int i, j;
 
@@ -917,7 +909,6 @@ void intel_gtt_insert_pages(unsigned int first_entry, unsigned int num_entries,
         }
         readl(intel_private.gtt+j-1);
 }
-EXPORT_SYMBOL(intel_gtt_insert_pages);
 
 static int intel_fake_agp_insert_entries(struct agp_memory *mem,
                                          off_t pg_start, int type)
@@ -953,13 +944,15 @@ static int intel_fake_agp_insert_entries(struct agp_memory *mem,
                 global_cache_flush();
 
         if (intel_private.base.needs_dmar) {
-                ret = intel_gtt_map_memory(mem->pages, mem->page_count,
-                                           &mem->sg_list, &mem->num_sg);
+                struct sg_table st;
+
+                ret = intel_gtt_map_memory(mem->pages, mem->page_count, &st);
                 if (ret != 0)
                         return ret;
 
-                intel_gtt_insert_sg_entries(mem->sg_list, mem->num_sg,
-                                            pg_start, type);
+                intel_gtt_insert_sg_entries(&st, pg_start, type);
+                mem->sg_list = st.sgl;
+                mem->num_sg = st.nents;
         } else
                 intel_gtt_insert_pages(pg_start, mem->page_count, mem->pages,
                                        type);