[PATCH v5 2/5] hw/cxl: Use switch statements for read and write of cachemem registers

[Jonathan Cameron via <qemu-devel@nongnu.org>]

Establishing that only register accesses of size 4 and 8 can occur
using these functions requires looking at their callers. Make it
easier to see that by using switch statements.
Assertions are used to enforce that the register storage is of the
matching size, allowing fixed values to be used for divisors of
the array indices.

Suggested-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>

---
v5: _Static_assert() is a declaration in C, so may not follow
    a label. Hence wrap it in {} to ensure it doesn't.
    Issue seen with clang builds (and in some cases at least older
    GCC).
    We can't wrap it in {} in the QEMU_BUILD_BUG_ON() define as that
    is used in a few places outside of functions.

hw/cxl/cxl-component-utils.c | 66 +++++++++++++++++++++++-------------
 1 file changed, 43 insertions(+), 23 deletions(-)

diff --git a/hw/cxl/cxl-component-utils.c b/hw/cxl/cxl-component-utils.c
index f3bbf0fd13..9d4f4bc8d4 100644
--- a/hw/cxl/cxl-component-utils.c
+++ b/hw/cxl/cxl-component-utils.c
@@ -67,16 +67,24 @@ static uint64_t cxl_cache_mem_read_reg(void *opaque, hwaddr offset,
     CXLComponentState *cxl_cstate = opaque;
     ComponentRegisters *cregs = &cxl_cstate->crb;
 
-    if (size == 8) {
+    switch (size) {
+    case 4:
+        if (cregs->special_ops && cregs->special_ops->read) {
+            return cregs->special_ops->read(cxl_cstate, offset, 4);
+        } else {
+            QEMU_BUILD_BUG_ON(sizeof(*cregs->cache_mem_registers) != 4);
+            return cregs->cache_mem_registers[offset / 4];
+        }
+    case 8:
         qemu_log_mask(LOG_UNIMP,
                       "CXL 8 byte cache mem registers not implemented\n");
         return 0;
-    }
-
-    if (cregs->special_ops && cregs->special_ops->read) {
-        return cregs->special_ops->read(cxl_cstate, offset, size);
-    } else {
-        return cregs->cache_mem_registers[offset / sizeof(*cregs->cache_mem_registers)];
+    default:
+        /*
+         * In line with specifiction limitaions on access sizes, this
+         * routine is not called with other sizes.
+         */
+        g_assert_not_reached();
     }
 }
 
@@ -117,25 +125,37 @@ static void cxl_cache_mem_write_reg(void *opaque, hwaddr offset, uint64_t value,
     ComponentRegisters *cregs = &cxl_cstate->crb;
     uint32_t mask;
 
-    if (size == 8) {
-        qemu_log_mask(LOG_UNIMP,
-                      "CXL 8 byte cache mem registers not implemented\n");
+    switch (size) {
+    case 4: {
+        QEMU_BUILD_BUG_ON(sizeof(*cregs->cache_mem_regs_write_mask) != 4);
+        QEMU_BUILD_BUG_ON(sizeof(*cregs->cache_mem_registers) != 4);
+        mask = cregs->cache_mem_regs_write_mask[offset / 4];
+        value &= mask;
+        /* RO bits should remain constant. Done by reading existing value */
+        value |= ~mask & cregs->cache_mem_registers[offset / 4];
+        if (cregs->special_ops && cregs->special_ops->write) {
+            cregs->special_ops->write(cxl_cstate, offset, value, size);
+            return;
+        }
+
+        if (offset >= A_CXL_HDM_DECODER_CAPABILITY &&
+            offset <= A_CXL_HDM_DECODER3_TARGET_LIST_HI) {
+            dumb_hdm_handler(cxl_cstate, offset, value);
+        } else {
+            cregs->cache_mem_registers[offset / 4] = value;
+        }
         return;
     }
-    mask = cregs->cache_mem_regs_write_mask[offset / sizeof(*cregs->cache_mem_regs_write_mask)];
-    value &= mask;
-    /* RO bits should remain constant. Done by reading existing value */
-    value |= ~mask & cregs->cache_mem_registers[offset / sizeof(*cregs->cache_mem_registers)];
-    if (cregs->special_ops && cregs->special_ops->write) {
-        cregs->special_ops->write(cxl_cstate, offset, value, size);
+    case 8:
+        qemu_log_mask(LOG_UNIMP,
+                      "CXL 8 byte cache mem registers not implemented\n");
         return;
-    }
-
-    if (offset >= A_CXL_HDM_DECODER_CAPABILITY &&
-        offset <= A_CXL_HDM_DECODER3_TARGET_LIST_HI) {
-        dumb_hdm_handler(cxl_cstate, offset, value);
-    } else {
-        cregs->cache_mem_registers[offset / sizeof(*cregs->cache_mem_registers)] = value;
+    default:
+        /*
+         * In line with specifiction limitaions on access sizes, this
+         * routine is not called with other sizes.
+         */
+        g_assert_not_reached();
     }
 }
 
-- 
2.39.2