ACPI: Page based coalescing of I/O remappings optimization

This patch optimizes ACPI MMIO remappings by keeping track of the
remappings on a PAGE_SIZE granularity.

When an ioremap() occurs, the underlying infrastructure works on a 'page'
based granularity.  As such, an ioremap() request for 1 byte for example,
will end up mapping in an entire (PAGE_SIZE) page.  Huang Ying took
advantage of this in commit 15651291a2f8c11e7e6a42d8bfde7a213ff13262 by
checking if subsequent ioremap() requests reside within any of the list's
existing remappings still in place, and if so, incrementing a reference
count on the existing mapping as opposed to performing another ioremap().

Signed-off-by: Myron Stowe <myron.stowe@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 51 insertions, 11 deletions

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 32826893c2e6..885e222bcabd 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -104,6 +104,7 @@ struct acpi_ioremap {
         void __iomem *virt;
         acpi_physical_address phys;
         acpi_size size;
+        struct kref ref;
 };
 
 static LIST_HEAD(acpi_ioremaps);
@@ -245,15 +246,28 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
 }
 
 /* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
-static void __iomem *
-acpi_map_vaddr_lookup(acpi_physical_address phys, acpi_size size)
+static struct acpi_ioremap *
+acpi_map_lookup(acpi_physical_address phys, acpi_size size)
 {
         struct acpi_ioremap *map;
 
         list_for_each_entry_rcu(map, &acpi_ioremaps, list)
                 if (map->phys <= phys &&
                     phys + size <= map->phys + map->size)
-                        return map->virt + (phys - map->phys);
+                        return map;
+
+        return NULL;
+}
+
+/* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
+static void __iomem *
+acpi_map_vaddr_lookup(acpi_physical_address phys, unsigned int size)
+{
+        struct acpi_ioremap *map;
+
+        map = acpi_map_lookup(phys, size);
+        if (map)
+                return map->virt + (phys - map->phys);
 
         return NULL;
 }
@@ -265,7 +279,8 @@ acpi_map_lookup_virt(void __iomem *virt, acpi_size size)
         struct acpi_ioremap *map;
 
         list_for_each_entry_rcu(map, &acpi_ioremaps, list)
-                if (map->virt == virt && map->size == size)
+                if (map->virt <= virt &&
+                    virt + size <= map->virt + map->size)
                         return map;
 
         return NULL;
@@ -274,9 +289,10 @@ acpi_map_lookup_virt(void __iomem *virt, acpi_size size)
 void __iomem *__init_refok
 acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
 {
-        struct acpi_ioremap *map;
-        unsigned long flags;
+        struct acpi_ioremap *map, *tmp_map;
+        unsigned long flags, pg_sz;
         void __iomem *virt;
+        phys_addr_t pg_off;
 
         if (phys > ULONG_MAX) {
                 printk(KERN_ERR PREFIX "Cannot map memory that high\n");
@@ -290,7 +306,9 @@ acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
         if (!map)
                 return NULL;
 
-        virt = ioremap(phys, size);
+        pg_off = round_down(phys, PAGE_SIZE);
+        pg_sz = round_up(phys + size, PAGE_SIZE) - pg_off;
+        virt = ioremap(pg_off, pg_sz);
         if (!virt) {
                 kfree(map);
                 return NULL;
@@ -298,21 +316,40 @@ acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
 
         INIT_LIST_HEAD(&map->list);
         map->virt = virt;
-        map->phys = phys;
-        map->size = size;
+        map->phys = pg_off;
+        map->size = pg_sz;
+        kref_init(&map->ref);
 
         spin_lock_irqsave(&acpi_ioremap_lock, flags);
+        /* Check if page has already been mapped. */
+        tmp_map = acpi_map_lookup(phys, size);
+        if (tmp_map) {
+                kref_get(&tmp_map->ref);
+                spin_unlock_irqrestore(&acpi_ioremap_lock, flags);
+                iounmap(map->virt);
+                kfree(map);
+                return tmp_map->virt + (phys - tmp_map->phys);
+        }
         list_add_tail_rcu(&map->list, &acpi_ioremaps);
         spin_unlock_irqrestore(&acpi_ioremap_lock, flags);
 
-        return virt;
+        return map->virt + (phys - map->phys);
 }
 EXPORT_SYMBOL_GPL(acpi_os_map_memory);
 
+static void acpi_kref_del_iomap(struct kref *ref)
+{
+        struct acpi_ioremap *map;
+
+        map = container_of(ref, struct acpi_ioremap, ref);
+        list_del_rcu(&map->list);
+}
+
 void __ref acpi_os_unmap_memory(void __iomem *virt, acpi_size size)
 {
         struct acpi_ioremap *map;
         unsigned long flags;
+        int del;
 
         if (!acpi_gbl_permanent_mmap) {
                 __acpi_unmap_table(virt, size);
@@ -328,9 +365,12 @@ void __ref acpi_os_unmap_memory(void __iomem *virt, acpi_size size)
                 return;
         }
 
-        list_del_rcu(&map->list);
+        del = kref_put(&map->ref, acpi_kref_del_iomap);
         spin_unlock_irqrestore(&acpi_ioremap_lock, flags);
 
+        if (!del)
+                return;
+
         synchronize_rcu();
         iounmap(map->virt);
         kfree(map);