[PATCH V3 1/2] iommu/ipmmu-vmsa: Use refcount for the micro-TLBs

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Reference-count the micro-TLBs as several bus masters can be
connected to the same micro-TLB (and drop TODO comment).
This wasn't an issue so far, since the platform devices
(this driver deals with) get assigned/deassigned together during
domain creation/destruction. But, in order to support PCI devices
(which are hot-pluggable) in the near future we will need to
take care of.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
---
Changes V1 -> V2:
   - add R-b
   - add ASSERT() in ipmmu_utlb_disable()

Changes V2 -> V3:
   - add comment to the code
---
 xen/drivers/passthrough/arm/ipmmu-vmsa.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/xen/drivers/passthrough/arm/ipmmu-vmsa.c 
b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
index 649b9f6..c912120 100644
--- a/xen/drivers/passthrough/arm/ipmmu-vmsa.c
+++ b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
@@ -127,6 +127,7 @@ struct ipmmu_vmsa_device {
     spinlock_t lock;    /* Protects ctx and domains[] */
     DECLARE_BITMAP(ctx, IPMMU_CTX_MAX);
     struct ipmmu_vmsa_domain *domains[IPMMU_CTX_MAX];
+    unsigned int utlb_refcount[IPMMU_UTLB_MAX];
     const struct ipmmu_features *features;
 };
 
@@ -468,12 +469,17 @@ static int ipmmu_utlb_enable(struct ipmmu_vmsa_domain 
*domain,
     }
 
     /*
-     * TODO: Reference-count the micro-TLB as several bus masters can be
-     * connected to the same micro-TLB.
+     * Reference-count the micro-TLBs as several bus masters can be connected
+     * to the same micro-TLB. The platform devices get assigned/deassigned
+     * together during domain creation/destruction. The PCI devices which use
+     * the same micro-TLB must also be hot-(un)plugged together.
      */
-    ipmmu_imuasid_write(mmu, utlb, 0);
-    ipmmu_imuctr_write(mmu, utlb, imuctr |
-                       IMUCTR_TTSEL_MMU(domain->context_id) | IMUCTR_MMUEN);
+    if ( mmu->utlb_refcount[utlb]++ == 0 )
+    {
+        ipmmu_imuasid_write(mmu, utlb, 0);
+        ipmmu_imuctr_write(mmu, utlb, imuctr |
+                           IMUCTR_TTSEL_MMU(domain->context_id) | 
IMUCTR_MMUEN);
+    }
 
     return 0;
 }
@@ -484,7 +490,10 @@ static void ipmmu_utlb_disable(struct ipmmu_vmsa_domain 
*domain,
 {
     struct ipmmu_vmsa_device *mmu = domain->mmu;
 
-    ipmmu_imuctr_write(mmu, utlb, 0);
+    ASSERT(mmu->utlb_refcount[utlb] > 0);
+
+    if ( --mmu->utlb_refcount[utlb] == 0 )
+        ipmmu_imuctr_write(mmu, utlb, 0);
 }
 
 /* Domain/Context Management */
-- 
2.7.4