[Xen-devel] [PATCH 4/4] AMD/IOMMU: Treat head/tail pointers as byte offsets

[Andrew Cooper <andrew.cooper3@citrix.com>]

The MMIO registers as already byte offsets.  Using them in this form removes
the need to shift their values for use.

It is also inefficient to store both entries and alloc_size (which differ by a
fixed entry_size).  Rename alloc_size to size, and drop entries entirely,
which simplifies the allocation/deallocation helpers slightly.

Mark send_iommu_command() and invalidate_iommu_all() as static, as they have
no external declaration or callers.

Overall, this simplification allows GCC to optimise sufficiently to construct
commands directly in the command ring, rather than on the stack and copying
them into place.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>

Tested on a Rome system.
---
 xen/drivers/passthrough/amd/iommu-defs.h |  1 -
 xen/drivers/passthrough/amd/iommu.h      | 18 ++----------------
 xen/drivers/passthrough/amd/iommu_cmd.c  | 20 ++++++++------------
 xen/drivers/passthrough/amd/iommu_init.c | 30 +++++++++++++-----------------
 4 files changed, 23 insertions(+), 46 deletions(-)

diff --git a/xen/drivers/passthrough/amd/iommu-defs.h b/xen/drivers/passthrough/amd/iommu-defs.h
index 963009de6a..50613ca150 100644
--- a/xen/drivers/passthrough/amd/iommu-defs.h
+++ b/xen/drivers/passthrough/amd/iommu-defs.h
@@ -481,7 +481,6 @@ struct amd_iommu_pte {
 #define INV_IOMMU_ALL_PAGES_ADDRESS      ((1ULL << 63) - 1)
 
 #define IOMMU_RING_BUFFER_PTR_MASK                  0x0007FFF0
-#define IOMMU_RING_BUFFER_PTR_SHIFT                 4
 
 #define IOMMU_CMD_DEVICE_ID_MASK                    0x0000FFFF
 #define IOMMU_CMD_DEVICE_ID_SHIFT                   0
diff --git a/xen/drivers/passthrough/amd/iommu.h b/xen/drivers/passthrough/amd/iommu.h
index 0b598d06f8..1abfdc685a 100644
--- a/xen/drivers/passthrough/amd/iommu.h
+++ b/xen/drivers/passthrough/amd/iommu.h
@@ -58,12 +58,11 @@ struct table_struct {
 };
 
 struct ring_buffer {
+    spinlock_t lock;    /* protect buffer pointers */
     void *buffer;
-    unsigned long entries;
-    unsigned long alloc_size;
     uint32_t tail;
     uint32_t head;
-    spinlock_t lock;    /* protect buffer pointers */
+    uint32_t size;
 };
 
 typedef struct iommu_cap {
@@ -379,19 +378,6 @@ static inline int iommu_has_cap(struct amd_iommu *iommu, uint32_t bit)
     return !!(iommu->cap.header & (1u << bit));
 }
 
-/* access tail or head pointer of ring buffer */
-static inline uint32_t iommu_get_rb_pointer(uint32_t reg)
-{
-    return get_field_from_reg_u32(reg, IOMMU_RING_BUFFER_PTR_MASK,
-                                  IOMMU_RING_BUFFER_PTR_SHIFT);
-}
-
-static inline void iommu_set_rb_pointer(uint32_t *reg, uint32_t val)
-{
-    set_field_in_reg_u32(val, *reg, IOMMU_RING_BUFFER_PTR_MASK,
-                         IOMMU_RING_BUFFER_PTR_SHIFT, reg);
-}
-
 /* access device id field from iommu cmd */
 static inline uint16_t iommu_get_devid_from_cmd(uint32_t cmd)
 {
diff --git a/xen/drivers/passthrough/amd/iommu_cmd.c b/xen/drivers/passthrough/amd/iommu_cmd.c
index 166f0e7263..24ef59d436 100644
--- a/xen/drivers/passthrough/amd/iommu_cmd.c
+++ b/xen/drivers/passthrough/amd/iommu_cmd.c
@@ -24,16 +24,14 @@ static int queue_iommu_command(struct amd_iommu *iommu, u32 cmd[])
 {
     uint32_t tail, head;
 
-    tail = iommu->cmd_buffer.tail;
-    if ( ++tail == iommu->cmd_buffer.entries )
+    tail = iommu->cmd_buffer.tail + IOMMU_CMD_BUFFER_ENTRY_SIZE;
+    if ( tail == iommu->cmd_buffer.size )
         tail = 0;
 
-    head = iommu_get_rb_pointer(readl(iommu->mmio_base +
-                                      IOMMU_CMD_BUFFER_HEAD_OFFSET));
+    head = readl(iommu->mmio_base + IOMMU_CMD_BUFFER_HEAD_OFFSET);
     if ( head != tail )
     {
-        memcpy(iommu->cmd_buffer.buffer +
-               (iommu->cmd_buffer.tail * IOMMU_CMD_BUFFER_ENTRY_SIZE),
+        memcpy(iommu->cmd_buffer.buffer + iommu->cmd_buffer.tail,
                cmd, IOMMU_CMD_BUFFER_ENTRY_SIZE);
 
         iommu->cmd_buffer.tail = tail;
@@ -45,13 +43,11 @@ static int queue_iommu_command(struct amd_iommu *iommu, u32 cmd[])
 
 static void commit_iommu_command_buffer(struct amd_iommu *iommu)
 {
-    u32 tail = 0;
-
-    iommu_set_rb_pointer(&tail, iommu->cmd_buffer.tail);
-    writel(tail, iommu->mmio_base+IOMMU_CMD_BUFFER_TAIL_OFFSET);
+    writel(iommu->cmd_buffer.tail,
+           iommu->mmio_base + IOMMU_CMD_BUFFER_TAIL_OFFSET);
 }
 
-int send_iommu_command(struct amd_iommu *iommu, u32 cmd[])
+static int send_iommu_command(struct amd_iommu *iommu, u32 cmd[])
 {
     if ( queue_iommu_command(iommu, cmd) )
     {
@@ -261,7 +257,7 @@ static void invalidate_interrupt_table(struct amd_iommu *iommu, u16 device_id)
     send_iommu_command(iommu, cmd);
 }
 
-void invalidate_iommu_all(struct amd_iommu *iommu)
+static void invalidate_iommu_all(struct amd_iommu *iommu)
 {
     u32 cmd[4], entry;
 
diff --git a/xen/drivers/passthrough/amd/iommu_init.c b/xen/drivers/passthrough/amd/iommu_init.c
index 7bf6fef3ee..cfdeeefc2d 100644
--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -117,7 +117,7 @@ static void register_iommu_cmd_buffer_in_mmio_space(struct amd_iommu *iommu)
     iommu_set_addr_lo_to_reg(&entry, addr_lo >> PAGE_SHIFT);
     writel(entry, iommu->mmio_base + IOMMU_CMD_BUFFER_BASE_LOW_OFFSET);
 
-    power_of2_entries = get_order_from_bytes(iommu->cmd_buffer.alloc_size) +
+    power_of2_entries = get_order_from_bytes(iommu->cmd_buffer.size) +
         IOMMU_CMD_BUFFER_POWER_OF2_ENTRIES_PER_PAGE;
 
     entry = 0;
@@ -145,7 +145,7 @@ static void register_iommu_event_log_in_mmio_space(struct amd_iommu *iommu)
     iommu_set_addr_lo_to_reg(&entry, addr_lo >> PAGE_SHIFT);
     writel(entry, iommu->mmio_base + IOMMU_EVENT_LOG_BASE_LOW_OFFSET);
 
-    power_of2_entries = get_order_from_bytes(iommu->event_log.alloc_size) +
+    power_of2_entries = get_order_from_bytes(iommu->event_log.size) +
                         IOMMU_EVENT_LOG_POWER_OF2_ENTRIES_PER_PAGE;
 
     entry = 0;
@@ -173,7 +173,7 @@ static void register_iommu_ppr_log_in_mmio_space(struct amd_iommu *iommu)
     iommu_set_addr_lo_to_reg(&entry, addr_lo >> PAGE_SHIFT);
     writel(entry, iommu->mmio_base + IOMMU_PPR_LOG_BASE_LOW_OFFSET);
 
-    power_of2_entries = get_order_from_bytes(iommu->ppr_log.alloc_size) +
+    power_of2_entries = get_order_from_bytes(iommu->ppr_log.size) +
                         IOMMU_PPR_LOG_POWER_OF2_ENTRIES_PER_PAGE;
 
     entry = 0;
@@ -300,7 +300,7 @@ static int iommu_read_log(struct amd_iommu *iommu,
                           unsigned int entry_size,
                           void (*parse_func)(struct amd_iommu *, u32 *))
 {
-    u32 tail, head, *entry, tail_offest, head_offset;
+    u32 tail, *entry, tail_offest, head_offset;
 
     BUG_ON(!iommu || ((log != &iommu->event_log) && (log != &iommu->ppr_log)));
     
@@ -316,22 +316,20 @@ static int iommu_read_log(struct amd_iommu *iommu,
         IOMMU_PPR_LOG_HEAD_OFFSET;
 
     tail = readl(iommu->mmio_base + tail_offest);
-    tail = iommu_get_rb_pointer(tail);
 
     while ( tail != log->head )
     {
         /* read event log entry */
-        entry = (u32 *)(log->buffer + log->head * entry_size);
+        entry = (u32 *)(log->buffer + log->head);
 
         parse_func(iommu, entry);
-        if ( ++log->head == log->entries )
+
+        log->head += entry_size;
+        if ( log->head == log->size )
             log->head = 0;
 
         /* update head pointer */
-        head = 0;
-        iommu_set_rb_pointer(&head, log->head);
-
-        writel(head, iommu->mmio_base + head_offset);
+        writel(log->head, iommu->mmio_base + head_offset);
     }
 
     spin_unlock(&log->lock);
@@ -1001,7 +999,7 @@ static void __init deallocate_buffer(void *buf, unsigned long sz)
 
 static void __init deallocate_ring_buffer(struct ring_buffer *ring_buf)
 {
-    deallocate_buffer(ring_buf->buffer, ring_buf->alloc_size);
+    deallocate_buffer(ring_buf->buffer, ring_buf->size);
     ring_buf->buffer = NULL;
     ring_buf->head = 0;
     ring_buf->tail = 0;
@@ -1036,11 +1034,9 @@ static void *__init allocate_ring_buffer(struct ring_buffer *ring_buf,
     ring_buf->tail = 0;
 
     spin_lock_init(&ring_buf->lock);
-    
-    ring_buf->alloc_size = PAGE_SIZE << get_order_from_bytes(entries *
-                                                             entry_size);
-    ring_buf->entries = ring_buf->alloc_size / entry_size;
-    ring_buf->buffer = allocate_buffer(ring_buf->alloc_size, name, clear);
+
+    ring_buf->size = PAGE_SIZE << get_order_from_bytes(entries * entry_size);
+    ring_buf->buffer = allocate_buffer(ring_buf->size, name, clear);
 
     return ring_buf->buffer;
 }
-- 
2.11.0


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