firmware: qcom_scm: Cleanup code in qcom_scm_assign_mem()

There are some questionable coding styles in this function. It looks
quite odd to deref a pointer with array indexing that only uses the
first element. Also, destroying an input/output variable halfway through
the function and then overwriting it on success is not clear. It's
better to use a local variable and the kernel macros to step through
each bit set in a bitmask and clearly show where outputs are set.

Cc: Ian Jackson <ian.jackson@citrix.com>
Cc: Julien Grall <julien.grall@arm.com>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Avaneesh Kumar Dwivedi <akdwived@codeaurora.org>
Tested-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
[bjorn: Changed for_each_set_bit() size to BITS_PER_LONG]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/firmware/qcom_scm.c

@@ -434,7 +434,8 @@ EXPORT_SYMBOL(qcom_scm_set_remote_state);
  */
 int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
 			unsigned int *srcvm,
-			struct qcom_scm_vmperm *newvm, int dest_cnt)
+			const struct qcom_scm_vmperm *newvm,
+			unsigned int dest_cnt)
 {
 	struct qcom_scm_current_perm_info *destvm;
 	struct qcom_scm_mem_map_info *mem_to_map;
@@ -449,11 +450,10 @@ int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
 	int next_vm;
 	__le32 *src;
 	void *ptr;
-	int ret;
-	int len;
-	int i;
+	int ret, i, b;
+	unsigned long srcvm_bits = *srcvm;
 
-	src_sz = hweight_long(*srcvm) * sizeof(*src);
+	src_sz = hweight_long(srcvm_bits) * sizeof(*src);
 	mem_to_map_sz = sizeof(*mem_to_map);
 	dest_sz = dest_cnt * sizeof(*destvm);
 	ptr_sz = ALIGN(src_sz, SZ_64) + ALIGN(mem_to_map_sz, SZ_64) +
@@ -466,28 +466,26 @@ int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
 
 	/* Fill source vmid detail */
 	src = ptr;
-	len = hweight_long(*srcvm);
-	for (i = 0; i < len; i++) {
-		src[i] = cpu_to_le32(ffs(*srcvm) - 1);
-		*srcvm ^= 1 << (ffs(*srcvm) - 1);
-	}
+	i = 0;
+	for_each_set_bit(b, &srcvm_bits, BITS_PER_LONG)
+		src[i++] = cpu_to_le32(b);
 
 	/* Fill details of mem buff to map */
 	mem_to_map = ptr + ALIGN(src_sz, SZ_64);
 	mem_to_map_phys = ptr_phys + ALIGN(src_sz, SZ_64);
-	mem_to_map[0].mem_addr = cpu_to_le64(mem_addr);
-	mem_to_map[0].mem_size = cpu_to_le64(mem_sz);
+	mem_to_map->mem_addr = cpu_to_le64(mem_addr);
+	mem_to_map->mem_size = cpu_to_le64(mem_sz);
 
 	next_vm = 0;
 	/* Fill details of next vmid detail */
 	destvm = ptr + ALIGN(mem_to_map_sz, SZ_64) + ALIGN(src_sz, SZ_64);
 	dest_phys = ptr_phys + ALIGN(mem_to_map_sz, SZ_64) + ALIGN(src_sz, SZ_64);
-	for (i = 0; i < dest_cnt; i++) {
-		destvm[i].vmid = cpu_to_le32(newvm[i].vmid);
-		destvm[i].perm = cpu_to_le32(newvm[i].perm);
-		destvm[i].ctx = 0;
-		destvm[i].ctx_size = 0;
-		next_vm |= BIT(newvm[i].vmid);
+	for (i = 0; i < dest_cnt; i++, destvm++, newvm++) {
+		destvm->vmid = cpu_to_le32(newvm->vmid);
+		destvm->perm = cpu_to_le32(newvm->perm);
+		destvm->ctx = 0;
+		destvm->ctx_size = 0;
+		next_vm |= BIT(newvm->vmid);
 	}
 
 	ret = __qcom_scm_assign_mem(__scm->dev, mem_to_map_phys, mem_to_map_sz,

include/linux/qcom_scm.h

@@ -49,8 +49,9 @@ extern int qcom_scm_pas_mem_setup(u32 peripheral, phys_addr_t addr,
 extern int qcom_scm_pas_auth_and_reset(u32 peripheral);
 extern int qcom_scm_pas_shutdown(u32 peripheral);
 extern int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
-			       unsigned int *src, struct qcom_scm_vmperm *newvm,
-			       int dest_cnt);
+			       unsigned int *src,
+			       const struct qcom_scm_vmperm *newvm,
+			       unsigned int dest_cnt);
 extern void qcom_scm_cpu_power_down(u32 flags);
 extern u32 qcom_scm_get_version(void);
 extern int qcom_scm_set_remote_state(u32 state, u32 id);
@@ -87,8 +88,8 @@ qcom_scm_pas_auth_and_reset(u32 peripheral) { return -ENODEV; }
 static inline int qcom_scm_pas_shutdown(u32 peripheral) { return -ENODEV; }
 static inline int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
 				      unsigned int *src,
-				      struct qcom_scm_vmperm *newvm,
-				      int dest_cnt) { return -ENODEV; }
+				      const struct qcom_scm_vmperm *newvm,
+				      unsigned int dest_cnt) { return -ENODEV; }
 static inline void qcom_scm_cpu_power_down(u32 flags) {}
 static inline u32 qcom_scm_get_version(void) { return 0; }
 static inline u32