Re: [PATCH v6 1/3] PCI: qcom: Override NO_SNOOP attribute for SA8775P RC

Manivannan Sadhasivam
2024-03-10T12:54:23Z

On Wed, Mar 06, 2024 at 06:41:10PM +0530, Mrinmay Sarkar wrote:
> 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.
>
> Signed-off-by: Mrinmay Sarkar <quic_msarkar@quicinc.com>

Minor nit below. With that addressed,

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

> ---
> drivers/pci/controller/dwc/pcie-qcom.c | 25 ++++++++++++++++++++++++-
> 1 file changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 2ce2a3b..d4c1e69 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/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
>
> @@ -117,6 +118,10 @@
> /* 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
>
> @@ -227,8 +232,14 @@ 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;
> };
>
> struct qcom_pcie {
> @@ -961,6 +972,13 @@ 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;
> +
> + /* Override NO_SNOOP attribute in TLP to enable cache snooping */

This comment is now redundant due to Kdoc of override_no_snoop.

- Mani

> + 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_hpc(pcie->pci);
>
> return 0;
> @@ -1334,6 +1352,11 @@ 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,
> };
> @@ -1630,7 +1653,7 @@ 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_1_9_0 },
> - { .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_1_9_0 },
> --
> 2.7.4
>

--
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