linux-kernel - Re: [PATCH v3 2/3] PCI: qcom: Add equalization settings for 16GT/s

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Message-ID: <20240422151625.GG9775@thinkpad>
Date: Mon, 22 Apr 2024 20:46:25 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Shashank Babu Chinta Venkata <quic_schintav@...cinc.com>
Cc: agross@...nel.org, andersson@...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>,
	Jingoo Han <jingoohan1@...il.com>,
	Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Serge Semin <fancer.lancer@...il.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.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 v3 2/3] PCI: qcom: Add equalization settings for 16GT/s

On Thu, Apr 18, 2024 at 05:09:35PM -0700, Shashank Babu Chinta Venkata wrote:

PCI: qcom: Add PCIe link equalization settings for 16 GT/s

> GEN3_RELATED_OFFSET is being used to determine data rate of shadow
> registers. Select data rate as 16GT/s and set appropriate equilization
> settings to improve link stability for 16GT/s data rate.
> 

How about:

'To improve the PCIe link stability while running at the rate of 16 GT/s, set
the appropriate link equalization settings for both RC and EP controllers.'

However, I don't understand the statement about 'GEN3_RELATED_OFFSET' and
'shadow registers'. Please reword it to make it understandable.

> Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@...cinc.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware.h  | 12 ++++++++
>  drivers/pci/controller/dwc/pcie-qcom-common.c | 30 +++++++++++++++++++
>  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, 49 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 26dae4837462..ad771bb52d29 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(n)		FIELD_PREP(GENMASK(3, 0), n)
> +#define GEN3_EQ_CONTROL_OFF_PHASE23_EXIT_MODE(n)	FIELD_PREP(BIT(4), n)
> +#define GEN3_EQ_CONTROL_OFF_PSET_REQ_VEC(n)	FIELD_PREP(GENMASK(23, 8), n)
> +#define GEN3_EQ_CONTROL_OFF_FOM_INC_INITIAL_EVAL(n)	FIELD_PREP(BIT(24), n)
> +
> +#define GEN3_EQ_FB_MODE_DIR_CHANGE_OFF          0x8ac
> +#define GEN3_EQ_FMDC_T_MIN_PHASE23(n)	FIELD_PREP(GENMASK(4, 0), n)
> +#define GEN3_EQ_FMDC_N_EVALS(n)		FIELD_PREP(GENMASK(9, 5), n)
> +#define GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA(n)	FIELD_PREP(GENMASK(13, 10), n)
> +#define GEN3_EQ_FMDC_MAX_POST_CUSROR_DELTA(n)	FIELD_PREP(GENMASK(17, 14), n)
> +
>  #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 dc2120ec5fef..a6f3eb4c3ee6 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-common.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c
> @@ -16,6 +16,36 @@
>  #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 is repurposed to be used with GEN4(16GT/s) rate
> +	 * as well based on RATE_SHADOW_SEL_MASK settings on this register.

Same comment as above.

> +	 */
> +	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);

Use FIELD_PREP()

> +	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(0) |

You are reading 'reg' above and then overwriting immediately.

> +		GEN3_EQ_FMDC_N_EVALS(0xD) |

'0xd'

> +		GEN3_EQ_FMDC_MAX_PRE_CUSROR_DELTA(0x5) |
> +		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(0) |

Same as above.

- Mani

-- 
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