The find_reg function was assuming that there is always at least one table in
reg_tables. It is not always true.

In case of VCS or VECS, the reg_tables is NULL and reg_table_count is 0,
implying that no register-accessing commands are allowed. However, the command
tables include commands such as MI_STORE_REGISTER_MEM. When trying to check
such command, the find_reg would dereference NULL pointer.

Now it will just return NULL meaning that the register was not found and the
command will be rejected.

Signed-off-by: Michal Srb <m...@suse.com>
---
 drivers/gpu/drm/i915/i915_cmd_parser.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c 
b/drivers/gpu/drm/i915/i915_cmd_parser.c
index 8ba932b22f7c..de7ec59433d1 100644
--- a/drivers/gpu/drm/i915/i915_cmd_parser.c
+++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
@@ -1038,7 +1038,7 @@ find_reg(const struct intel_engine_cs *engine, bool 
is_master, u32 addr)
        const struct drm_i915_reg_table *table = engine->reg_tables;
        int count = engine->reg_table_count;
 
-       do {
+       for (; count > 0; ++table, --count) {
                if (!table->master || is_master) {
                        const struct drm_i915_reg_descriptor *reg;
 
@@ -1046,7 +1046,7 @@ find_reg(const struct intel_engine_cs *engine, bool 
is_master, u32 addr)
                        if (reg != NULL)
                                return reg;
                }
-       } while (table++, --count);
+       }
 
        return NULL;
 }
-- 
2.13.6

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