[PATCH v2] drm/panthor: use local variables for firmware interface counts

[Osama Abdelkader <osama.abdelkader@gmail.com>]

panthor_fw_init_ifaces() validates the firmware interface group count
before iterating over the CSG interfaces. panthor_init_csg_iface() does
the same for the per-group stream count before iterating over the CS
interfaces.

Store those validated counts in local variables and use the locals as the
loop bounds. This avoids reading the same control interface fields twice
and makes it explicit that the loops use the values that were just
validated.

Signed-off-by: Osama Abdelkader <osama.abdelkader@gmail.com>
Reviewed-by: Steven Price <steven.price@arm.com>
---
v2:
- Reword as an optimization/cleanup instead of a firmware trust-boundary fix.
- Drop the Fixes and stable tags.

 drivers/gpu/drm/panthor/panthor_fw.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
index e2fcbd639c3c..6e6da98d795e 100644
--- a/drivers/gpu/drm/panthor/panthor_fw.c
+++ b/drivers/gpu/drm/panthor/panthor_fw.c
@@ -959,6 +959,7 @@ static int panthor_init_csg_iface(struct panthor_device *ptdev,
 	u64 shared_section_sz = panthor_kernel_bo_size(ptdev->fw->shared_section->mem);
 	u64 iface_offset = CSF_GROUP_CONTROL_OFFSET +
 			   ((u64)csg_idx * glb_iface->control->group_stride);
+	u32 stream_num;
 	unsigned int i;
 
 	if (iface_offset > shared_section_sz ||
@@ -972,8 +973,8 @@ static int panthor_init_csg_iface(struct panthor_device *ptdev,
 	csg_iface->output = iface_fw_to_cpu_addr(ptdev, csg_iface->control->output_va,
 						 sizeof(*csg_iface->output));
 
-	if (csg_iface->control->stream_num < MIN_CS_PER_CSG ||
-	    csg_iface->control->stream_num > MAX_CS_PER_CSG)
+	stream_num = READ_ONCE(csg_iface->control->stream_num);
+	if (stream_num < MIN_CS_PER_CSG || stream_num > MAX_CS_PER_CSG)
 		return -EINVAL;
 
 	if (!csg_iface->input || !csg_iface->output) {
@@ -990,7 +991,7 @@ static int panthor_init_csg_iface(struct panthor_device *ptdev,
 		}
 	}
 
-	for (i = 0; i < csg_iface->control->stream_num; i++) {
+	for (i = 0; i < stream_num; i++) {
 		int ret = panthor_init_cs_iface(ptdev, csg_idx, i);
 
 		if (ret)
@@ -1015,6 +1016,7 @@ static int panthor_fw_init_ifaces(struct panthor_device *ptdev)
 {
 	struct panthor_fw_global_iface *glb_iface = &ptdev->fw->iface.global;
 	u64 shared_section_sz = panthor_kernel_bo_size(ptdev->fw->shared_section->mem);
+	u32 group_num;
 	unsigned int i;
 
 	if (!ptdev->fw->shared_section->mem->kmap)
@@ -1034,17 +1036,17 @@ static int panthor_fw_init_ifaces(struct panthor_device *ptdev)
 		return -EINVAL;
 	}
 
-	if (glb_iface->control->group_num > MAX_CSGS ||
-	    glb_iface->control->group_num < MIN_CSGS) {
+	group_num = READ_ONCE(glb_iface->control->group_num);
+	if (group_num > MAX_CSGS || group_num < MIN_CSGS) {
 		drm_err(&ptdev->base, "Invalid number of control groups");
 		return -EINVAL;
 	}
 
-	for (i = 0; i < glb_iface->control->group_num; i++) {
+	for (i = 0; i < group_num; i++) {
 		int ret = panthor_init_csg_iface(ptdev, i);
 
 		if (ret)
 			return ret;
 	}
 
 	drm_info(&ptdev->base, "CSF FW using interface v%d.%d.%d, Features %#x Instrumentation features %#x",
-- 
2.43.0