drm/amdgpu: fix NAK-G generation during PCI-e link width switch

A lot of NAK-G being generated when link widht switching is happening.
WA for this issue is to program the SPC to 4 symbols per clock during
bootup when the native PCIE width is x4.
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/amd/amdgpu/amdgpu_nbio.h

@@ -93,6 +93,7 @@ struct amdgpu_nbio_funcs {
 	void (*enable_aspm)(struct amdgpu_device *adev,
 			    bool enable);
 	void (*program_aspm)(struct amdgpu_device *adev);
+	void (*apply_lc_spc_mode_wa)(struct amdgpu_device *adev);
 };
 
 struct amdgpu_nbio {

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

@@ -51,6 +51,8 @@
 #define mmBIF_MMSCH1_DOORBELL_RANGE		0x01d8
 #define mmBIF_MMSCH1_DOORBELL_RANGE_BASE_IDX	2
 
+#define smnPCIE_LC_LINK_WIDTH_CNTL		0x11140288
+
 static void nbio_v2_3_remap_hdp_registers(struct amdgpu_device *adev)
 {
 	WREG32_SOC15(NBIO, 0, mmREMAP_HDP_MEM_FLUSH_CNTL,
@@ -463,6 +465,31 @@ static void nbio_v2_3_program_aspm(struct amdgpu_device *adev)
 		WREG32_PCIE(smnPCIE_LC_CNTL3, data);
 }
 
+static void nbio_v2_3_apply_lc_spc_mode_wa(struct amdgpu_device *adev)
+{
+	uint32_t reg_data = 0;
+	uint32_t link_width = 0;
+
+	if (!((adev->asic_type >= CHIP_NAVI10) &&
+	     (adev->asic_type <= CHIP_NAVI12)))
+		return;
+
+	reg_data = RREG32_PCIE(smnPCIE_LC_LINK_WIDTH_CNTL);
+	link_width = (reg_data & PCIE_LC_LINK_WIDTH_CNTL__LC_LINK_WIDTH_RD_MASK)
+		>> PCIE_LC_LINK_WIDTH_CNTL__LC_LINK_WIDTH_RD__SHIFT;
+
+	/*
+	 * Program PCIE_LC_CNTL6.LC_SPC_MODE_8GT to 0x2 (4 symbols per clock data)
+	 * if link_width is 0x3 (x4)
+	 */
+	if (0x3 == link_width) {
+		reg_data = RREG32_PCIE(smnPCIE_LC_CNTL6);
+		reg_data &= ~PCIE_LC_CNTL6__LC_SPC_MODE_8GT_MASK;
+		reg_data |= (0x2 << PCIE_LC_CNTL6__LC_SPC_MODE_8GT__SHIFT);
+		WREG32_PCIE(smnPCIE_LC_CNTL6, reg_data);
+	}
+}
+
 const struct amdgpu_nbio_funcs nbio_v2_3_funcs = {
 	.get_hdp_flush_req_offset = nbio_v2_3_get_hdp_flush_req_offset,
 	.get_hdp_flush_done_offset = nbio_v2_3_get_hdp_flush_done_offset,
@@ -484,4 +511,5 @@ const struct amdgpu_nbio_funcs nbio_v2_3_funcs = {
 	.remap_hdp_registers = nbio_v2_3_remap_hdp_registers,
 	.enable_aspm = nbio_v2_3_enable_aspm,
 	.program_aspm =  nbio_v2_3_program_aspm,
+	.apply_lc_spc_mode_wa = nbio_v2_3_apply_lc_spc_mode_wa,
 };

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

@@ -1411,6 +1411,9 @@ static int nv_common_hw_init(void *handle)
 {
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 
+	if (adev->nbio.funcs->apply_lc_spc_mode_wa)
+		adev->nbio.funcs->apply_lc_spc_mode_wa(adev);
+
 	/* enable pcie gen2/3 link */
 	nv_pcie_gen3_enable(adev);
 	/* enable aspm */