linux-kernel - Re: [PATCH 2/2] PCI: dwc: Add support to disable equalization phase 2 and 3

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Date:   Tue, 10 Sep 2019 15:05:02 +0100
From:   Andrew Murray <andrew.murray@....com>
To:     Pankaj Dubey <pankaj.dubey@...sung.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
        lorenzo.pieralisi@....com, bhelgaas@...gle.com,
        Anvesh Salveru <anvesh.s@...sung.com>
Subject: Re: [PATCH 2/2] PCI: dwc: Add support to disable equalization phase
 2 and 3

On Tue, Sep 10, 2019 at 05:55:02PM +0530, Pankaj Dubey wrote:
> From: Anvesh Salveru <anvesh.s@...sung.com>
> 
> In some platforms, PCIe PHY may have issues which will prevent linkup
> to happen in GEN3 or high speed. In case equalization fails, link will
> fallback to GEN1.
> 
> Designware controller gives flexibility to disable GEN3 equalization
> completely or only phase 2 and 3.

Do some platforms have issues conducting phase 2 and 3 when they successfully
conduct phase 0 and 1?

> 
> Platform drivers can disable equalization phase 2 and 3, by setting
> dwc_pci_quirk flag DWC_EQUALIZATION_DISABLE.
> 
> Signed-off-by: Anvesh Salveru <anvesh.s@...sung.com>
> Signed-off-by: Pankaj Dubey <pankaj.dubey@...sung.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware.c | 3 +++
>  drivers/pci/controller/dwc/pcie-designware.h | 2 ++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index bf82091..97a8268 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -472,5 +472,8 @@ void dw_pcie_setup(struct dw_pcie *pci)
>  	if (pci->dwc_pci_quirk & DWC_EQUALIZATION_DISABLE)
>  		val |= PORT_LOGIC_GEN3_EQ_DISABLE;
>  
> +	if (pci->dwc_pci_quirk & DWC_EQ_PHASE_2_3_DISABLE)
> +		val |= PORT_LOGIC_GEN3_EQ_PHASE_2_3_DISABLE;
> +
>  	dw_pcie_writel_dbi(pci, PCIE_PORT_GEN3_RELATED, val);
>  }
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index a1453c5..b541508 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -31,6 +31,7 @@
>  
>  /* Parameters for PCIe Quirks */
>  #define DWC_EQUALIZATION_DISABLE	0x1
> +#define DWC_EQ_PHASE_2_3_DISABLE	0x2

It only makes sense for either DWC_EQUALIZATION_DISABLE or DWC_EQ_PHASE_2_3_DISABLE
to be specified, though if dwc_pci_quirk intends to hold other quirks should these
be numbers and not bit fields?

Thanks,

Andrew Murray

>  
>  /* Synopsys-specific PCIe configuration registers */
>  #define PCIE_PORT_LINK_CONTROL		0x710
> @@ -65,6 +66,7 @@
>  
>  #define PCIE_PORT_GEN3_RELATED		0x890
>  #define PORT_LOGIC_GEN3_EQ_DISABLE	BIT(16)
> +#define PORT_LOGIC_GEN3_EQ_PHASE_2_3_DISABLE	BIT(9)
>  
>  #define PCIE_ATU_VIEWPORT		0x900
>  #define PCIE_ATU_REGION_INBOUND		BIT(31)
> -- 
> 2.7.4
>