iommu/ipmmu-vmsa: Add helper functions for MMU "context" registers

This is a non-verbatim port of corresponding Linux upsteam commit:
16d9454f5e0447f9c19cbf350b35ed377b9f64eb

Original commit message:
 commit 16d9454f5e0447f9c19cbf350b35ed377b9f64eb
 Author: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
 Date:   Wed Nov 6 11:35:47 2019 +0900

  iommu/ipmmu-vmsa: Add helper functions for MMU "context" registers

  Since we will have changed memory mapping of the IPMMU in the future,
  This patch adds helper functions ipmmu_ctx_{reg,read,write}()
  for MMU "context" registers. No behavior change.

  Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
  Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
  Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
  Signed-off-by: Joerg Roedel <jroedel@suse.de>

**********

This is a prereq work needed to add support for S4 series easily
in the future.

Besides changes done in the original commit, we also need to update
an extra call sites which Linux driver doesn't have, but Xen driver
has such as ipmmu_ctx_write_cache(), etc.

No change in behavior.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Julien Grall <jgrall@amazon.com>

xen/drivers/passthrough/arm/ipmmu-vmsa.c

@@ -307,18 +307,35 @@ static void ipmmu_write(struct ipmmu_vmsa_device *mmu, uint32_t offset,
     writel(data, mmu->base + offset);
 }
 
+static unsigned int ipmmu_ctx_reg(struct ipmmu_vmsa_device *mmu,
+                                  unsigned int context_id, uint32_t reg)
+{
+    return context_id * IM_CTX_SIZE + reg;
+}
+
+static uint32_t ipmmu_ctx_read(struct ipmmu_vmsa_device *mmu,
+                               unsigned int context_id, uint32_t reg)
+{
+    return ipmmu_read(mmu, ipmmu_ctx_reg(mmu, context_id, reg));
+}
+
+static void ipmmu_ctx_write(struct ipmmu_vmsa_device *mmu,
+                            unsigned int context_id, uint32_t reg,
+                            uint32_t data)
+{
+    ipmmu_write(mmu, ipmmu_ctx_reg(mmu, context_id, reg), data);
+}
+
 static uint32_t ipmmu_ctx_read_root(struct ipmmu_vmsa_domain *domain,
                                     uint32_t reg)
 {
-    return ipmmu_read(domain->mmu->root,
-                      domain->context_id * IM_CTX_SIZE + reg);
+    return ipmmu_ctx_read(domain->mmu->root, domain->context_id, reg);
 }
 
 static void ipmmu_ctx_write_root(struct ipmmu_vmsa_domain *domain,
                                  uint32_t reg, uint32_t data)
 {
-    ipmmu_write(domain->mmu->root,
-                domain->context_id * IM_CTX_SIZE + reg, data);
+    ipmmu_ctx_write(domain->mmu->root, domain->context_id, reg, data);
 }
 
 static void ipmmu_ctx_write_cache(struct ipmmu_vmsa_domain *domain,
@@ -329,8 +346,8 @@ static void ipmmu_ctx_write_cache(struct ipmmu_vmsa_domain *domain,
 
     /* Mask fields which are implemented in IPMMU-MM only. */
     if ( !ipmmu_is_root(domain->mmu) )
-        ipmmu_write(domain->mmu, domain->context_id * IM_CTX_SIZE + reg,
-                    data & IMCTR_COMMON_MASK);
+        ipmmu_ctx_write(domain->mmu, domain->context_id, reg,
+                        data & IMCTR_COMMON_MASK);
 }
 
 /*
@@ -693,7 +710,7 @@ static void ipmmu_device_reset(struct ipmmu_vmsa_device *mmu)
 
     /* Disable all contexts. */
     for ( i = 0; i < mmu->num_ctx; ++i )
-        ipmmu_write(mmu, i * IM_CTX_SIZE + IMCTR, 0);
+        ipmmu_ctx_write(mmu, i, IMCTR, 0);
 }
 
 /* R-Car Gen3 SoCs product and cut information. */