drm/amdgpu: Don't enable LTR if not supported

As per PCIE Base Spec r4.0 Section 6.18
'Software must not enable LTR in an Endpoint unless the Root Complex
and all intermediate Switches indicate support for LTR.'

This fixes the Unsupported Request error reported through AER during
ASPM enablement.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216455

The error was unnoticed before and got visible because of the commit
referenced below. This doesn't fix anything in the commit below, rather
fixes the issue in amdgpu exposed by the commit. The reference is only
to associate this commit with below one so that both go together.

Fixes: 8795e182b02d ("PCI/portdrv: Don't disable AER reporting in get_port_device_capability()")

Reported-by: Gustaw Smolarczyk <[e-mail]>
Signed-off-by: Lijo Lazar <[e-mail]>
Reviewed-by: Alex Deucher <[e-mail]>

Cc: [e-mail]
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/nbio_v2_3.c

···
 		WREG32_PCIE(smnPCIE_LC_CNTL, data);
 }
 
+#ifdef CONFIG_PCIEASPM
 static void nbio_v2_3_program_ltr(struct amdgpu_device *adev)
 {
 	uint32_t def, data;
···
 	if (def != data)
 		WREG32_PCIE(smnBIF_CFG_DEV0_EPF0_DEVICE_CNTL2, data);
 }
+#endif
 
 static void nbio_v2_3_program_aspm(struct amdgpu_device *adev)
 {
+#ifdef CONFIG_PCIEASPM
 	uint32_t def, data;
 
 	def = data = RREG32_PCIE(smnPCIE_LC_CNTL);
···
 	if (def != data)
 		WREG32_PCIE(smnPCIE_LC_CNTL6, data);
 
-	nbio_v2_3_program_ltr(adev);
+	/* Don't bother about LTR if LTR is not enabled
+	 * in the path */
+	if (adev->pdev->ltr_path)
+		nbio_v2_3_program_ltr(adev);
 
 	def = data = RREG32_SOC15(NBIO, 0, mmRCC_BIF_STRAP3);
 	data |= 0x5DE0 << RCC_BIF_STRAP3__STRAP_VLINK_ASPM_IDLE_TIMER__SHIFT;
···
 	data &= ~PCIE_LC_CNTL3__LC_DSC_DONT_ENTER_L23_AFTER_PME_ACK_MASK;
 	if (def != data)
 		WREG32_PCIE(smnPCIE_LC_CNTL3, data);
+#endif
 }
 
 static void nbio_v2_3_apply_lc_spc_mode_wa(struct amdgpu_device *adev)

drivers/gpu/drm/amd/amdgpu/nbio_v6_1.c

···
 			mmBIF_BX_DEV0_EPF0_VF0_HDP_MEM_COHERENCY_FLUSH_CNTL) << 2;
 }
 
+#ifdef CONFIG_PCIEASPM
 static void nbio_v6_1_program_ltr(struct amdgpu_device *adev)
 {
 	uint32_t def, data;
···
 	if (def != data)
 		WREG32_PCIE(smnBIF_CFG_DEV0_EPF0_DEVICE_CNTL2, data);
 }
+#endif
 
 static void nbio_v6_1_program_aspm(struct amdgpu_device *adev)
 {
+#ifdef CONFIG_PCIEASPM
 	uint32_t def, data;
 
 	def = data = RREG32_PCIE(smnPCIE_LC_CNTL);
···
 	if (def != data)
 		WREG32_PCIE(smnPCIE_LC_CNTL6, data);
 
-	nbio_v6_1_program_ltr(adev);
+	/* Don't bother about LTR if LTR is not enabled
+	 * in the path */
+	if (adev->pdev->ltr_path)
+		nbio_v6_1_program_ltr(adev);
 
 	def = data = RREG32_PCIE(smnRCC_BIF_STRAP3);
 	data |= 0x5DE0 << RCC_BIF_STRAP3__STRAP_VLINK_ASPM_IDLE_TIMER__SHIFT;
···
 	data &= ~PCIE_LC_CNTL3__LC_DSC_DONT_ENTER_L23_AFTER_PME_ACK_MASK;
 	if (def != data)
 		WREG32_PCIE(smnPCIE_LC_CNTL3, data);
+#endif
 }
 
 const struct amdgpu_nbio_funcs nbio_v6_1_funcs = {

drivers/gpu/drm/amd/amdgpu/nbio_v7_4.c

···
 };
 
 
+#ifdef CONFIG_PCIEASPM
 static void nbio_v7_4_program_ltr(struct amdgpu_device *adev)
 {
 	uint32_t def, data;
···
 	if (def != data)
 		WREG32_PCIE(smnBIF_CFG_DEV0_EPF0_DEVICE_CNTL2, data);
 }
+#endif
 
 static void nbio_v7_4_program_aspm(struct amdgpu_device *adev)
 {
+#ifdef CONFIG_PCIEASPM
 	uint32_t def, data;
 
 	if (adev->ip_versions[NBIO_HWIP][0] == IP_VERSION(7, 4, 4))
···
 	if (def != data)
 		WREG32_PCIE(smnPCIE_LC_CNTL6, data);
 
-	nbio_v7_4_program_ltr(adev);
+	/* Don't bother about LTR if LTR is not enabled
+	 * in the path */
+	if (adev->pdev->ltr_path)
+		nbio_v7_4_program_ltr(adev);
 
 	def = data = RREG32_PCIE(smnRCC_BIF_STRAP3);
 	data |= 0x5DE0 << RCC_BIF_STRAP3__STRAP_VLINK_ASPM_IDLE_TIMER__SHIFT;
···
 	data &= ~PCIE_LC_CNTL3__LC_DSC_DONT_ENTER_L23_AFTER_PME_ACK_MASK;
 	if (def != data)
 		WREG32_PCIE(smnPCIE_LC_CNTL3, data);
+#endif
 }
 
 const struct amdgpu_nbio_funcs nbio_v7_4_funcs = {