linux-kernel - Re: [PATCH v4 2/3] PCI: qcom: Add equalization settings for 16 GT/s

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Date: Thu, 30 May 2024 20:01:29 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Shashank Babu Chinta Venkata <quic_schintav@...cinc.com>
Cc: jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
	manivannan.sadhasivam@...aro.org, andersson@...nel.org,
	agross@...nel.org, konrad.dybcio@...aro.org,
	quic_msarkar@...cinc.com, quic_kraravin@...cinc.com,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Serge Semin <fancer.lancer@...il.com>,
	Conor Dooley <conor.dooley@...rochip.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 2/3] PCI: qcom: Add equalization settings for 16 GT/s

On Wed, May 01, 2024 at 09:35:33AM -0700, Shashank Babu Chinta Venkata wrote:
> During high data transmission rates such as 16 GT/s , there is an
> increased risk of signal loss due to poor channel quality and
> interference. This can impact receiver's ability to capture signals
> accurately. Hence, signal compensation is achieved through appropriate
> lane equilization settings at both transmitter and receiver. This will
> result in increasing PCIe signal strength.

s/increasing/increased

> 
> Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@...cinc.com>

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

- Mani

> ---
>  drivers/pci/controller/dwc/pcie-designware.h  | 12 ++++++
>  drivers/pci/controller/dwc/pcie-qcom-common.c | 37 +++++++++++++++++++
>  drivers/pci/controller/dwc/pcie-qcom-common.h |  1 +
>  drivers/pci/controller/dwc/pcie-qcom-ep.c     |  3 ++
>  drivers/pci/controller/dwc/pcie-qcom.c        |  3 ++
>  5 files changed, 56 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 26dae4837462..ed0045043847 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -122,6 +122,18 @@
>  #define GEN3_RELATED_OFF_RATE_SHADOW_SEL_SHIFT	24
>  #define GEN3_RELATED_OFF_RATE_SHADOW_SEL_MASK	GENMASK(25, 24)
>  
> +#define GEN3_EQ_CONTROL_OFF			0x8a8
> +#define GEN3_EQ_CONTROL_OFF_FB_MODE		GENMASK(3, 0)
> +#define GEN3_EQ_CONTROL_OFF_PHASE23_EXIT_MODE	BIT(4)
> +#define GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC	GENMASK(23, 8)
> +#define GEN3_EQ_CONTROL_OFF_FOM_INC_INITIAL_EVAL	BIT(24)
> +
> +#define GEN3_EQ_FB_MODE_DIR_CHANGE_OFF          0x8ac
> +#define GEN3_EQ_FMDC_T_MIN_PHASE23		GENMASK(4, 0)
> +#define GEN3_EQ_FMDC_N_EVALS			GENMASK(9, 5)
> +#define GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA	GENMASK(13, 10)
> +#define GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA	GENMASK(17, 14)
> +
>  #define PCIE_PORT_MULTI_LANE_CTRL	0x8C0
>  #define PORT_MLTI_UPCFG_SUPPORT		BIT(7)
>  
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.c b/drivers/pci/controller/dwc/pcie-qcom-common.c
> index 228d9eec0222..16c277b2e9d4 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-common.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c
> @@ -16,6 +16,43 @@
>  #define QCOM_PCIE_LINK_SPEED_TO_BW(speed) \
>  		Mbps_to_icc(PCIE_SPEED2MBS_ENC(pcie_link_speed[speed]))
>  
> +void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci)
> +{
> +	u32 reg;
> +
> +	/*
> +	 * GEN3_RELATED_OFF register is repurposed to apply equilaztion
> +	 * settings at various data transmission rates through registers
> +	 * namely GEN3_EQ_*. RATE_SHADOW_SEL bit field of GEN3_RELATED_OFF
> +	 * determines data rate for which this equilization settings are
> +	 * applied.
> +	 */
> +	reg = dw_pcie_readl_dbi(pci, GEN3_RELATED_OFF);
> +	reg &= ~GEN3_RELATED_OFF_GEN3_ZRXDC_NONCOMPL;
> +	reg &= ~GEN3_RELATED_OFF_RATE_SHADOW_SEL_MASK;
> +	reg |= FIELD_PREP(GEN3_RELATED_OFF_RATE_SHADOW_SEL_MASK, 0x1);
> +	dw_pcie_writel_dbi(pci, GEN3_RELATED_OFF, reg);
> +
> +	reg = dw_pcie_readl_dbi(pci, GEN3_EQ_FB_MODE_DIR_CHANGE_OFF);
> +	reg &= ~(GEN3_EQ_FMDC_T_MIN_PHASE23 |
> +		GEN3_EQ_FMDC_N_EVALS |
> +		GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA |
> +		GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA);
> +	reg |= FIELD_PREP(GEN3_EQ_FMDC_T_MIN_PHASE23, 0x1) |
> +		FIELD_PREP(GEN3_EQ_FMDC_N_EVALS, 0xd) |
> +		FIELD_PREP(GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA, 0x5) |
> +		FIELD_PREP(GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA, 0x5);
> +	dw_pcie_writel_dbi(pci, GEN3_EQ_FB_MODE_DIR_CHANGE_OFF, reg);
> +
> +	reg = dw_pcie_readl_dbi(pci, GEN3_EQ_CONTROL_OFF);
> +	reg &= ~(GEN3_EQ_CONTROL_OFF_FB_MODE |
> +		GEN3_EQ_CONTROL_OFF_PHASE23_EXIT_MODE |
> +		GEN3_EQ_CONTROL_OFF_FOM_INC_INITIAL_EVAL |
> +		GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC);
> +	dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, reg);
> +}
> +EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_eq_settings);
> +
>  struct icc_path *qcom_pcie_common_icc_get_resource(struct dw_pcie *pci, const char *path)
>  {
>  	struct icc_path *icc_mem_p;
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.h b/drivers/pci/controller/dwc/pcie-qcom-common.h
> index da1760c7e164..5c01f6c18b3b 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-common.h
> +++ b/drivers/pci/controller/dwc/pcie-qcom-common.h
> @@ -10,3 +10,4 @@
>  struct icc_path *qcom_pcie_common_icc_get_resource(struct dw_pcie *pci, const char *path);
>  int qcom_pcie_common_icc_init(struct dw_pcie *pci, struct icc_path *icc_mem);
>  void qcom_pcie_common_icc_update(struct dw_pcie *pci, struct icc_path *icc_mem);
> +void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci);
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> index f0c61d847643..7940222d35f6 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> @@ -438,6 +438,9 @@ static int qcom_pcie_perst_deassert(struct dw_pcie *pci)
>  		goto err_disable_resources;
>  	}
>  
> +	if (pcie_link_speed[pci->link_gen] == PCIE_SPEED_16_0GT)
> +		qcom_pcie_common_set_16gt_eq_settings(pci);
> +
>  	/*
>  	 * The physical address of the MMIO region which is exposed as the BAR
>  	 * should be written to MHI BASE registers.
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 0095c42aeee0..525942f2cf98 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -263,6 +263,9 @@ static int qcom_pcie_start_link(struct dw_pcie *pci)
>  {
>  	struct qcom_pcie *pcie = to_qcom_pcie(pci);
>  
> +	if (pcie_link_speed[pci->link_gen] == PCIE_SPEED_16_0GT)
> +		qcom_pcie_common_set_16gt_eq_settings(pci);
> +
>  	/* Enable Link Training state machine */
>  	if (pcie->cfg->ops->ltssm_enable)
>  		pcie->cfg->ops->ltssm_enable(pcie);
> -- 
> 2.43.2
> 

-- 
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