Re: [PATCH v3 3/3] PCI: qcom: Add rx margining settings for 16GT/s

[Konrad Dybcio]

On 4/19/24 02:09, Shashank Babu Chinta Venkata wrote:
> Add rx lane margining settings for 16GT/s(GEN 4) data rate. These
> settings improve link stability while operating at high date rates
> and helps to improve signal quality.
>
> Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@xxxxxxxxxxx>
> ---
>   drivers/pci/controller/dwc/pcie-designware.h  | 18 ++++++++++++++
>   drivers/pci/controller/dwc/pcie-qcom-common.c | 24 +++++++++++++++++++
>   drivers/pci/controller/dwc/pcie-qcom-common.h |  1 +
>   drivers/pci/controller/dwc/pcie-qcom-ep.c     |  4 +++-
>   drivers/pci/controller/dwc/pcie-qcom.c        |  4 +++-
>   5 files changed, 49 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index ad771bb52d29..e8c48855143f 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -203,6 +203,24 @@
>   
>   #define PCIE_PL_CHK_REG_ERR_ADDR			0xB28
>   
> +/*
> + * GEN4 lane margining register definitions
> + */
> +#define GEN4_LANE_MARGINING_1_OFF		0xb80
> +#define MARGINING_MAX_VOLTAGE_OFFSET(n)		FIELD_PREP(GENMASK(29, 24), n)
> +#define MARGINING_NUM_VOLTAGE_STEPS(n)		FIELD_PREP(GENMASK(22, 16), n)
> +#define MARGINING_MAX_TIMING_OFFSET(n)		FIELD_PREP(GENMASK(13, 8), n)
> +#define MARGINING_NUM_TIMING_STEPS(n)		FIELD_PREP(GENMASK(5, 0), n)
> +
> +#define GEN4_LANE_MARGINING_2_OFF		0xb84
> +#define MARGINING_IND_ERROR_SAMPLER(n)		FIELD_PREP(BIT(28), n)
> +#define MARGINING_SAMPLE_REPORTING_METHOD(n)	FIELD_PREP(BIT(27), n)
> +#define MARGINING_IND_LEFT_RIGHT_TIMING(n)	FIELD_PREP(BIT(26), n)
> +#define MARGINING_IND_UP_DOWN_VOLTAGE(n)	FIELD_PREP(BIT(25), n)
> +#define MARGINING_VOLTAGE_SUPPORTED(n)		FIELD_PREP(BIT(24), n)
> +#define MARGINING_MAXLANES(n)			FIELD_PREP(GENMASK(20, 16), n)
> +#define MARGINING_SAMPLE_RATE_TIMING(n)		FIELD_PREP(GENMASK(13, 8), n)
> +#define MARGINING_SAMPLE_RATE_VOLTAGE(n)	FIELD_PREP(GENMASK(5, 0), n)

That's a.. rather unusual.. use of FIELD_/GENMASK.. Usually, the fields are
defined with GENMASK and then referenced through FIELD_xyz(BITFIELD_NAME, val)

That said, I'm not entirely against this if Mani is ok with it

>   /*
>    * iATU Unroll-specific register definitions
>    * From 4.80 core version the address translation will be made by unroll
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.c b/drivers/pci/controller/dwc/pcie-qcom-common.c
> index a6f3eb4c3ee6..3279314ae78c 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-common.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c
> @@ -46,6 +46,30 @@ void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci)
>   }
>   EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_eq_settings);
>   
> +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci)
> +{
> +	u32 reg;
> +
> +	reg = dw_pcie_readl_dbi(pci, GEN4_LANE_MARGINING_1_OFF);
> +	reg = MARGINING_MAX_VOLTAGE_OFFSET(0x24) |
> +		MARGINING_NUM_VOLTAGE_STEPS(0x78) |
> +		MARGINING_MAX_TIMING_OFFSET(0x32) |
> +		MARGINING_NUM_TIMING_STEPS(0x10);
> +	dw_pcie_writel_dbi(pci, GEN4_LANE_MARGINING_1_OFF, reg);

Since this is DW-common, why is this inside the qcom driver?

Konrad