drm/amd/display: Fix NULL pointer dereference for DTN log in DCN401

When users run the command:

cat /sys/kernel/debug/dri/0/amdgpu_dm_dtn_log

The following NULL pointer dereference happens:

[  +0.000003] BUG: kernel NULL pointer dereference, address: NULL
[  +0.000005] #PF: supervisor instruction fetch in kernel mode
[  +0.000002] #PF: error_code(0x0010) - not-present page
[  +0.000002] PGD 0 P4D 0
[  +0.000004] Oops: 0010 [#1] PREEMPT SMP NOPTI
[  +0.000003] RIP: 0010:0x0
[  +0.000008] Code: Unable to access opcode bytes at 0xffffffffffffffd6.
[...]
[  +0.000002] PKRU: 55555554
[  +0.000002] Call Trace:
[  +0.000002]  <TASK>
[  +0.000003]  ? show_regs+0x65/0x70
[  +0.000006]  ? __die+0x24/0x70
[  +0.000004]  ? page_fault_oops+0x160/0x470
[  +0.000006]  ? do_user_addr_fault+0x2b5/0x690
[  +0.000003]  ? prb_read_valid+0x1c/0x30
[  +0.000005]  ? exc_page_fault+0x8c/0x1a0
[  +0.000005]  ? asm_exc_page_fault+0x27/0x30
[  +0.000012]  dcn10_log_color_state+0xf9/0x510 [amdgpu]
[  +0.000306]  ? srso_alias_return_thunk+0x5/0xfbef5
[  +0.000003]  ? vsnprintf+0x2fb/0x600
[  +0.000009]  dcn10_log_hw_state+0xfd0/0xfe0 [amdgpu]
[  +0.000218]  ? __mod_memcg_lruvec_state+0xe8/0x170
[  +0.000008]  ? srso_alias_return_thunk+0x5/0xfbef5
[  +0.000002]  ? debug_smp_processor_id+0x17/0x20
[  +0.000003]  ? srso_alias_return_thunk+0x5/0xfbef5
[  +0.000002]  ? srso_alias_return_thunk+0x5/0xfbef5
[  +0.000002]  ? set_ptes.isra.0+0x2b/0x90
[  +0.000004]  ? srso_alias_return_thunk+0x5/0xfbef5
[  +0.000002]  ? _raw_spin_unlock+0x19/0x40
[  +0.000004]  ? srso_alias_return_thunk+0x5/0xfbef5
[  +0.000002]  ? do_anonymous_page+0x337/0x700
[  +0.000004]  dtn_log_read+0x82/0x120 [amdgpu]
[  +0.000207]  full_proxy_read+0x66/0x90
[  +0.000007]  vfs_read+0xb0/0x340
[  +0.000005]  ? __count_memcg_events+0x79/0xe0
[  +0.000002]  ? srso_alias_return_thunk+0x5/0xfbef5
[  +0.000003]  ? count_memcg_events.constprop.0+0x1e/0x40
[  +0.000003]  ? handle_mm_fault+0xb2/0x370
[  +0.000003]  ksys_read+0x6b/0xf0
[  +0.000004]  __x64_sys_read+0x19/0x20
[  +0.000003]  do_syscall_64+0x60/0x130
[  +0.000004]  entry_SYSCALL_64_after_hwframe+0x6e/0x76
[  +0.000003] RIP: 0033:0x7fdf32f147e2
[...]

This error happens when the color log tries to read the gamut remap
information from DCN401 which is not initialized in the dcn401_dpp_funcs
which leads to a null pointer dereference. This commit addresses this
issue by adding a proper guard to access the gamut_remap callback in
case the specific ASIC did not implement this function.
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/hwss/dcn10/dcn10_hwseq.c

@@ -289,6 +289,7 @@ static void dcn10_log_color_state(struct dc *dc,
 {
 	struct dc_context *dc_ctx = dc->ctx;
 	struct resource_pool *pool = dc->res_pool;
+	bool is_gamut_remap_available = false;
 	int i;
 
 	DTN_INFO("DPP:    IGAM format    IGAM mode    DGAM mode    RGAM mode"
@@ -301,16 +302,15 @@ static void dcn10_log_color_state(struct dc *dc,
 		struct dcn_dpp_state s = {0};
 
 		dpp->funcs->dpp_read_state(dpp, &s);
+		if (dpp->funcs->dpp_get_gamut_remap) {
 			dpp->funcs->dpp_get_gamut_remap(dpp, &s.gamut_remap);
+			is_gamut_remap_available = true;
+		}
 
 		if (!s.is_enabled)
 			continue;
 
-		DTN_INFO("[%2d]:  %11xh  %11s    %9s    %9s"
-			 "  %12s  "
-			 "%010lld %010lld %010lld %010lld "
-			 "%010lld %010lld %010lld %010lld "
-			 "%010lld %010lld %010lld %010lld",
+		DTN_INFO("[%2d]:  %11xh  %11s    %9s    %9s",
 				dpp->inst,
 				s.igam_input_format,
 				(s.igam_lut_mode == 0) ? "BypassFixed" :
@@ -329,10 +329,14 @@ static void dcn10_log_color_state(struct dc *dc,
 					((s.rgam_lut_mode == 2) ? "Ycc" :
 					((s.rgam_lut_mode == 3) ? "RAM" :
 					((s.rgam_lut_mode == 4) ? "RAM" :
-								 "Unknown")))),
+								 "Unknown")))));
+		if (is_gamut_remap_available)
+			DTN_INFO("  %12s  "
+				 "%010lld %010lld %010lld %010lld "
+				 "%010lld %010lld %010lld %010lld "
+				 "%010lld %010lld %010lld %010lld",
 				 (s.gamut_remap.gamut_adjust_type == 0) ? "Bypass" :
-					((s.gamut_remap.gamut_adjust_type == 1) ? "HW" :
-										  "SW"),
+					((s.gamut_remap.gamut_adjust_type == 1) ? "HW" : "SW"),
 				 s.gamut_remap.temperature_matrix[0].value,
 				 s.gamut_remap.temperature_matrix[1].value,
 				 s.gamut_remap.temperature_matrix[2].value,
@@ -345,6 +349,7 @@ static void dcn10_log_color_state(struct dc *dc,
 				 s.gamut_remap.temperature_matrix[9].value,
 				 s.gamut_remap.temperature_matrix[10].value,
 				 s.gamut_remap.temperature_matrix[11].value);
+
 		DTN_INFO("\n");
 	}
 	DTN_INFO("\n");