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Date: Tue, 2 Apr 2024 11:15:38 +0530
From: Manivannan Sadhasivam <mani@kernel.org>
To: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com>
Cc: agross@kernel.org, andersson@kernel.org, konrad.dybcio@linaro.org,
	quic_msarkar@quicinc.com, quic_kraravin@quicinc.com,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>,
	Rob Herring <robh@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
	Jingoo Han <jingoohan1@gmail.com>,
	Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	Serge Semin <fancer.lancer@gmail.com>,
	Conor Dooley <conor.dooley@microchip.com>,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH v2 2/3] PCI: qcom: Add equalization settings for gen4
Message-ID: <20240402054538.GJ2933@thinkpad>
References: <20240320071527.13443-1-quic_schintav@quicinc.com>
 <20240320071527.13443-3-quic_schintav@quicinc.com>
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In-Reply-To: <20240320071527.13443-3-quic_schintav@quicinc.com>

On Wed, Mar 20, 2024 at 12:14:46AM -0700, Shashank Babu Chinta Venkata wrote:

Here, you are referring to 16 GT/s as the Gen4 datarate. So please mention that
explicitly.

> GEN3_RELATED_OFFSET is being used as shadow register for generation4 and

What is 'GEN3_RELATED_OFFSET' register? Where it is defined? More info on this
register would be helpful.

> generation5 data rates based on rate select mask settings on this register.

Please reword this sentence to make it more readable.

> Select relevant mask and equalization settings for generation4 operation.
> 
> Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware.h | 15 ++++++++
>  drivers/pci/controller/dwc/pcie-qcom-cmn.c   | 36 ++++++++++++++++++++
>  drivers/pci/controller/dwc/pcie-qcom-cmn.h   |  5 +++
>  drivers/pci/controller/dwc/pcie-qcom-ep.c    |  3 ++
>  drivers/pci/controller/dwc/pcie-qcom.c       |  3 ++
>  5 files changed, 62 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 26dae4837462..064744bfe35a 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -122,6 +122,21 @@
>  #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_MASK        GENMASK(3, 0)
> +#define GEN3_EQ_CONTROL_OFF_PHASE23_EXIT_MODE   BIT(4)
> +#define GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC_MASK	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_MASK         GENMASK(4, 0)
> +#define GEN3_EQ_FMDC_N_EVALS_MASK               GENMASK(9, 5)
> +#define GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA_MASK  GENMASK(13, 10)
> +#define GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA_MASK	GENMASK(17, 14)
> +#define GEN3_EQ_FMDC_N_EVALS_SHIFT			5
> +#define GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA_SHIFT		10
> +#define GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA_SHIFT	14
> +

You are adding the definitions in designware header, but funtion definitions in
Qcom driver. Does this mean, this configuration is specific to Qcom and not
applicable to other DWC drivers?

>  #define PCIE_PORT_MULTI_LANE_CTRL	0x8C0
>  #define PORT_MLTI_UPCFG_SUPPORT		BIT(7)
>  
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-cmn.c b/drivers/pci/controller/dwc/pcie-qcom-cmn.c
> index 64fa412ec293..208a55e8e9a1 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-cmn.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom-cmn.c
> @@ -17,6 +17,42 @@
>  #define QCOM_PCIE_LINK_SPEED_TO_BW(speed) \
>  		Mbps_to_icc(PCIE_SPEED2MBS_ENC(pcie_link_speed[speed]))
>  
> +void qcom_pcie_cmn_set_16gt_eq_settings(struct dw_pcie *pci)
> +{
> +	u32 reg;
> +
> +	/*
> +	 * GEN3_RELATED_OFF is repurposed to be used with GEN4(16GT/s) rate
> +	 * as well based on RATE_SHADOW_SEL_MASK settings on this register.
> +	 */
> +	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 |= (0x1 << GEN3_RELATED_OFF_RATE_SHADOW_SEL_SHIFT);

Please use FIELD_* macros where applicable.

> +	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_MASK;
> +	reg &= ~GEN3_EQ_FMDC_N_EVALS_MASK;
> +	reg |= (GEN3_EQ_FMDC_N_EVALS_16GT_VAL <<
> +		GEN3_EQ_FMDC_N_EVALS_SHIFT);
> +	reg &= ~GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA_MASK;
> +	reg |= (GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA_16GT_VAL <<
> +		GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA_SHIFT);
> +	reg &= ~GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA_MASK;
> +	reg |= (GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA_16GT_VAL <<
> +		GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA_SHIFT);
> +	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_MASK;
> +	reg &= ~GEN3_EQ_CONTROL_OFF_PHASE23_EXIT_MODE;
> +	reg &= ~GEN3_EQ_CONTROL_OFF_FOM_INC_INITIAL_EVAL;
> +	reg &= ~GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC_MASK;
> +	dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, reg);
> +}
> +EXPORT_SYMBOL_GPL(qcom_pcie_cmn_set_16gt_eq_settings);
> +
>  int qcom_pcie_cmn_icc_get_resource(struct dw_pcie *pci, struct icc_path *icc_mem)
>  {
>  	if (IS_ERR(pci))
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-cmn.h b/drivers/pci/controller/dwc/pcie-qcom-cmn.h
> index 845eda23ae59..97302e8fafa8 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-cmn.h
> +++ b/drivers/pci/controller/dwc/pcie-qcom-cmn.h
> @@ -9,6 +9,11 @@
>  #include "../../pci.h"
>  #include "pcie-designware.h"
>  
> +#define GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA_16GT_VAL   0x5
> +#define GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA_16GT_VAL  0x5
> +#define GEN3_EQ_FMDC_N_EVALS_16GT_VAL          0xD
> +

So these settings are Qcom specific? I'd expect this to be documented in commit
message.

>  int qcom_pcie_cmn_icc_get_resource(struct dw_pcie *pci, struct icc_path *icc_mem);
>  int qcom_pcie_cmn_icc_init(struct dw_pcie *pci, struct icc_path *icc_mem);
>  void qcom_pcie_cmn_icc_update(struct dw_pcie *pci, struct icc_path *icc_mem);
> +void qcom_pcie_cmn_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 ce6343426de8..b6bcab21bb9f 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_cmn_set_16gt_eq_settings(pci);

So this relies on the optional 'max-link-speed' DT property, but not mentioned
in the commit message :/

- Mani

> +
>  	/*
>  	 * 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 57a08294c561..b0a22a000fa3 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_cmn_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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