Re: [PATCH v6 3/4] PCI: qcom: Add equalization settings for 16.0 GT/s

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Wed, Sep 04, 2024 at 11:39:09AM +0200, Johan Hovold wrote:
> On Wed, Sep 04, 2024 at 12:41:59PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> > From: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com>
> > 
> > During high data transmission rates such as 16.0 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 equalization
> > settings at both transmitter and receiver. This will result in increased
> > PCIe signal strength.
> > 
> > Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com>
> > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > [mani: dropped the code refactoring and minor changes]
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
>  
> > +#define GEN3_EQ_CONTROL_OFF			0x8a8
> 
> Nit: uppercase hex since that's what is used for the other offsets
> 
> > +#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
> 
> Nit: odd indentation uses spaces, uppercase
> 
> > +#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
> > new file mode 100644
> > index 000000000000..dc7d93db9dc5
> > --- /dev/null
> > +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c
> > @@ -0,0 +1,45 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
> > + */
> > +
> > +#include <linux/pci.h>
> > +
> > +#include "pcie-designware.h"
> > +#include "pcie-qcom-common.h"
> > +
> > +void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci)
> > +{
> > +	u32 reg;
> > +
> > +	/*
> > +	 * GEN3_RELATED_OFF register is repurposed to apply equalization
> > +	 * 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 equalization settings are applied.
> 
> *The* RATE_SHADOW_SEL bit field
> 
> *the* data rate
> 
> s/this/these/
> 
> > +	 */
> > +	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);
> 
> How does 0x1 map to gen4/16 GT?
> 

I need inputs from Shashank here as I don't know the answer.

- Mani

> > +	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);
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.h b/drivers/pci/controller/dwc/pcie-qcom-common.h
> > new file mode 100644
> > index 000000000000..259e04b7bdf9
> > --- /dev/null
> > +++ b/drivers/pci/controller/dwc/pcie-qcom-common.h
> > @@ -0,0 +1,8 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
> > + */
> > +
> > +#include "pcie-designware.h"
> 
> You only need a forward declaration:
> 
> 	struct dw_pcie;
> 
> > +
> > +void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci);
> 
> Compile guard still missing.
> 
> Johan

-- 
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