drm/msm: Avoid NULL dereference in msm_disp_state_print_regs()

If the allocation in msm_disp_state_dump_regs() failed then
`block->state` can be NULL. The msm_disp_state_print_regs() function
_does_ have code to try to handle it with:

  if (*reg)
    dump_addr = *reg;

...but since "dump_addr" is initialized to NULL the above is actually
a noop. The code then goes on to dereference `dump_addr`.

Make the function print "Registers not stored" when it sees a NULL to
solve this. Since we're touching the code, fix
msm_disp_state_print_regs() not to pointlessly take a double-pointer
and properly mark the pointer as `const`.

Fixes: 98659487b845 ("drm/msm: add support to take dpu snapshot")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/619657/
Link: https://lore.kernel.org/r/20241014093605.1.Ia1217cecec9ef09eb3c6d125360cc6c8574b0e73@changeid
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>

diff --git a/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c b/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
index add72bb..bb14928 100644 (file)
--- a/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
+++ b/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
@@ -48,20 +48,21 @@ static void msm_disp_state_dump_regs(u32 **reg, u32 aligned_len, void __iomem *b
        }
 }
 
-static void msm_disp_state_print_regs(u32 **reg, u32 len, void __iomem *base_addr,
-               struct drm_printer *p)
+static void msm_disp_state_print_regs(const u32 *dump_addr, u32 len,
+               void __iomem *base_addr, struct drm_printer *p)
 {
        int i;
-       u32 *dump_addr = NULL;
        void __iomem *addr;
        u32 num_rows;
 
+       if (!dump_addr) {
+               drm_printf(p, "Registers not stored\n");
+               return;
+       }
+
        addr = base_addr;
        num_rows = len / REG_DUMP_ALIGN;
 
-       if (*reg)
-               dump_addr = *reg;
-
        for (i = 0; i < num_rows; i++) {
                drm_printf(p, "0x%lx : %08x %08x %08x %08x\n",
                                (unsigned long)(addr - base_addr),
@@ -89,7 +90,7 @@ void msm_disp_state_print(struct msm_disp_state *state, struct drm_printer *p)
 
        list_for_each_entry_safe(block, tmp, &state->blocks, node) {
                drm_printf(p, "====================%s================\n", block->name);
-               msm_disp_state_print_regs(&block->state, block->size, block->base_addr, p);
+               msm_disp_state_print_regs(block->state, block->size, block->base_addr, p);
        }
 
        drm_printf(p, "===================dpu drm state================\n");