PCI: qcom: Override NO_SNOOP attribute for SA8775P RC

Due to some hardware changes, SA8775P has set the NO_SNOOP attribute
in its TLP for all the PCIe controllers. NO_SNOOP attribute when set,
the requester is indicating that no cache coherency issue exist for
the addressed memory on the endpoint i.e., memory is not cached. But
in reality, requester cannot assume this unless there is a complete
control/visibility over the addressed memory on the endpoint.

And worst case, if the memory is cached on the endpoint, it may lead to
memory corruption issues. It should be noted that the caching of memory
on the endpoint is not solely dependent on the NO_SNOOP attribute in TLP.

So to avoid the corruption, this patch overrides the NO_SNOOP attribute
by setting the PCIE_PARF_NO_SNOOP_OVERIDE register. This patch is not
needed for other upstream supported platforms since they do not set
NO_SNOOP attribute by default.

8775 has IP version 1.34.0 so introduce a new cfg(cfg_1_34_0) for this
platform. Assign override_no_snoop flag into struct qcom_pcie_cfg and
set it true in cfg_1_34_0 and enable cache snooping if this particular
flag is true.

Link: https://lore.kernel.org/linux-pci/[email protected]
Signed-off-by: Mrinmay Sarkar <[email protected]>
Signed-off-by: Krzysztof Wilczyński <[email protected]>
[bhelgaas: wrap comments to fit in 80 columns]
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Manivannan Sadhasivam <[email protected]>

Author: Mrinmay Sarkar

drivers/pci/controller/dwc/pcie-qcom.c

@@ -51,6 +51,7 @@
 #define PARF_SID_OFFSET				0x234
 #define PARF_BDF_TRANSLATE_CFG			0x24c
 #define PARF_SLV_ADDR_SPACE_SIZE		0x358
+#define PARF_NO_SNOOP_OVERIDE			0x3d4
 #define PARF_DEVICE_TYPE			0x1000
 #define PARF_BDF_TO_SID_TABLE_N			0x2000
 #define PARF_BDF_TO_SID_CFG			0x2c00
@@ -118,6 +119,10 @@
 /* PARF_LTSSM register fields */
 #define LTSSM_EN				BIT(8)
 
+/* PARF_NO_SNOOP_OVERIDE register fields */
+#define WR_NO_SNOOP_OVERIDE_EN			BIT(1)
+#define RD_NO_SNOOP_OVERIDE_EN			BIT(3)
+
 /* PARF_DEVICE_TYPE register fields */
 #define DEVICE_TYPE_RC				0x4
 
@@ -229,8 +234,15 @@ struct qcom_pcie_ops {
 	int (*config_sid)(struct qcom_pcie *pcie);
 };
 
+ /**
+  * struct qcom_pcie_cfg - Per SoC config struct
+  * @ops: qcom PCIe ops structure
+  * @override_no_snoop: Override NO_SNOOP attribute in TLP to enable cache
+  * snooping
+  */
 struct qcom_pcie_cfg {
 	const struct qcom_pcie_ops *ops;
+	bool override_no_snoop;
 	bool no_l0s;
 };
 
@@ -930,6 +942,12 @@ static int qcom_pcie_init_2_7_0(struct qcom_pcie *pcie)
 
 static int qcom_pcie_post_init_2_7_0(struct qcom_pcie *pcie)
 {
+	const struct qcom_pcie_cfg *pcie_cfg = pcie->cfg;
+
+	if (pcie_cfg->override_no_snoop)
+		writel(WR_NO_SNOOP_OVERIDE_EN | RD_NO_SNOOP_OVERIDE_EN,
+				pcie->parf + PARF_NO_SNOOP_OVERIDE);
+
 	qcom_pcie_clear_aspm_l0s(pcie->pci);
 	qcom_pcie_clear_hpc(pcie->pci);
 
@@ -1305,6 +1323,11 @@ static const struct qcom_pcie_cfg cfg_1_9_0 = {
 	.ops = &ops_1_9_0,
 };
 
+static const struct qcom_pcie_cfg cfg_1_34_0 = {
+	.ops = &ops_1_9_0,
+	.override_no_snoop = true,
+};
+
 static const struct qcom_pcie_cfg cfg_2_1_0 = {
 	.ops = &ops_2_1_0,
 };
@@ -1606,7 +1629,7 @@ static const struct of_device_id qcom_pcie_match[] = {
 	{ .compatible = "qcom,pcie-msm8996", .data = &cfg_2_3_2 },
 	{ .compatible = "qcom,pcie-qcs404", .data = &cfg_2_4_0 },
 	{ .compatible = "qcom,pcie-sa8540p", .data = &cfg_sc8280xp },
-	{ .compatible = "qcom,pcie-sa8775p", .data = &cfg_1_9_0},
+	{ .compatible = "qcom,pcie-sa8775p", .data = &cfg_1_34_0},
 	{ .compatible = "qcom,pcie-sc7280", .data = &cfg_1_9_0 },
 	{ .compatible = "qcom,pcie-sc8180x", .data = &cfg_1_9_0 },
 	{ .compatible = "qcom,pcie-sc8280xp", .data = &cfg_sc8280xp },