[PATCH] drm/amd/display: Fix null pointer for res_pool->hubbub

[Bob Zhou]

Recently, the driver introduce DML2 for future ASIC support.
But, some ASIC's hubbub pointer isn't set after calling
dce120_create_resource_pool(). Before setting get_dchub_ref_freq(),
these hubbub pointer is null, it cause the below null pointer issue.
So add check whether res_pool->hubbub to fix it.

BUG: kernel NULL pointer dereference, address: 0000000000000000
RIP: 0010:dc_create_resource_pool+0xc1/0x2c0 [amdgpu]
Call Trace:
 <TASK>
 ? show_regs.cold+0x1a/0x1f
 ? __die_body+0x20/0x70
 ? __die+0x2b/0x37
 ? page_fault_oops+0x136/0x2c0
 ? do_user_addr_fault+0x303/0x660
 ? exc_page_fault+0x77/0x170
 ? asm_exc_page_fault+0x27/0x30
 ? dc_create_resource_pool+0xc1/0x2c0 [amdgpu]
 ? dc_create_resource_pool+0x243/0x2c0 [amdgpu]
 dc_create+0x23f/0x6b0 [amdgpu]
 ? dmi_matches+0xa3/0x200
 amdgpu_dm_init+0x2bd/0x22a0 [amdgpu]

Fixes: 50003b5aa5f5 ("drm/amd/display: Introduce DML2")
Signed-off-by: Bob Zhou <bob.zhou at amd.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_resource.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
index a93db60fe4d9..9cc7a001f9a1 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
@@ -319,10 +319,12 @@ struct resource_pool *dc_create_resource_pool(struct dc  *dc,
 				res_pool->ref_clocks.xtalin_clock_inKhz;
 			res_pool->ref_clocks.dchub_ref_clock_inKhz =
 				res_pool->ref_clocks.xtalin_clock_inKhz;
-			if ((res_pool->hubbub->funcs->get_dchub_ref_freq))
-				res_pool->hubbub->funcs->get_dchub_ref_freq(res_pool->hubbub,
-					res_pool->ref_clocks.dccg_ref_clock_inKhz,
-					&res_pool->ref_clocks.dchub_ref_clock_inKhz);
+			if (res_pool->hubbub)
+				if (res_pool->hubbub->funcs->get_dchub_ref_freq)
+					res_pool->hubbub->funcs->get_dchub_ref_freq(
+						res_pool->hubbub,
+						res_pool->ref_clocks.dccg_ref_clock_inKhz,
+						&res_pool->ref_clocks.dchub_ref_clock_inKhz);
 		} else
 			ASSERT_CRITICAL(false);
 	}
-- 
2.34.1