linux-kernel - Re: [PATCH V1 2/2] PCI: designware-ep: Disable PTM capabilities for EP mode

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Message-ID: <20221028165753.GA897928@bhelgaas>
Date:   Fri, 28 Oct 2022 11:57:53 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
        lpieralisi@...nel.org, robh@...nel.org, kw@...ux.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, kthota@...dia.com,
        mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V1 2/2] PCI: designware-ep: Disable PTM capabilities for
 EP mode

On Mon, Sep 19, 2022 at 08:03:40PM +0530, Vidya Sagar wrote:
> Dual mode DesignWare PCIe IP has PTM capability enabled (if supported) even
> in the EP mode. The PCIe compliance for the EP mode expects PTM
> capabilities (ROOT_CAPABLE, RES_CAPABLE, CLK_GRAN) be disabled.
> Hence disable PTM for the EP mode.
> 
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
>  .../pci/controller/dwc/pcie-designware-ep.c   | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index 7e9529ae3824..dc3057b18f36 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -646,7 +646,7 @@ int dw_pcie_ep_init_complete(struct dw_pcie_ep *ep)
>  	struct dw_pcie_ep_func *ep_func;
>  	struct device *dev = pci->dev;
>  	struct pci_epc *epc = ep->epc;
> -	unsigned int offset;
> +	unsigned int offset, ptm_cap_base;
>  	unsigned int nbars;
>  	u8 hdr_type;
>  	u8 func_no;
> @@ -698,6 +698,7 @@ int dw_pcie_ep_init_complete(struct dw_pcie_ep *ep)
>  	}
>  
>  	offset = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_REBAR);
> +	ptm_cap_base = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_PTM);
>  
>  	dw_pcie_dbi_ro_wr_en(pci);
>  
> @@ -710,6 +711,22 @@ int dw_pcie_ep_init_complete(struct dw_pcie_ep *ep)
>  			dw_pcie_writel_dbi(pci, offset + PCI_REBAR_CAP, 0x0);
>  	}
>  
> +	/*
> +	 * PTM responder capability can be disabled only after disabling
> +	 * PTM root capability.
> +	 */
> +	if (ptm_cap_base) {
> +		dw_pcie_dbi_ro_wr_en(pci);
> +		reg = dw_pcie_readl_dbi(pci, ptm_cap_base + PCI_PTM_CAP);
> +		reg &= ~PCI_PTM_CAP_ROOT;
> +		dw_pcie_writel_dbi(pci, ptm_cap_base + PCI_PTM_CAP, reg);
> +
> +		reg = dw_pcie_readl_dbi(pci, ptm_cap_base + PCI_PTM_CAP);
> +		reg &= ~(PCI_PTM_CAP_RES | PCI_PTM_GRANULARITY_MASK);
> +		dw_pcie_writel_dbi(pci, ptm_cap_base + PCI_PTM_CAP, reg);
> +		dw_pcie_dbi_ro_wr_dis(pci);

Per spec, PTM Responder Capable, PTM Root Capable, and Local Clock
Granularity may only be set for Root Ports, RCRBs, and Switches (PCIe
r6.0, sec 7.9.15.2).

And this is just a matter of making an Endpoint comply with the spec,
i.e., configures the Endpoint so it doesn't advertise that it can be a
PTM Responder, right?

But the Endpoint probably still *can* be a PTM Requester?

> +	}
> +
>  	dw_pcie_setup(pci);
>  	dw_pcie_dbi_ro_wr_dis(pci);
>  
> -- 
> 2.17.1
>