linux-kernel - Re: [PATCH v4 4/4] PCI: qcom: Enable ECAM feature

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Message-ID: <20250210225431.GA21989@bhelgaas>
Date: Mon, 10 Feb 2025 16:54:31 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: cros-qcom-dts-watchers@...omium.org,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jingoo Han <jingoohan1@...il.com>, linux-arm-msm@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, quic_vbadigan@...cinc.com,
	quic_mrana@...cinc.com, quic_vpernami@...cinc.com,
	mmareddy@...cinc.com
Subject: Re: [PATCH v4 4/4] PCI: qcom: Enable ECAM feature

On Fri, Feb 07, 2025 at 04:58:59AM +0530, Krishna Chaitanya Chundru wrote:
> The ELBI registers falls after the DBI space, PARF_SLV_DBI_ELBI register
> gives us the offset from which ELBI starts. so use this offset and cfg
> win to map these regions instead of doing the ioremap again.

> +	/* Set the ECAM base */
> +	writel_relaxed(lower_32_bits(pci->dbi_phys_addr), pcie->parf + PARF_ECAM_BASE);
> +	writel_relaxed(upper_32_bits(pci->dbi_phys_addr), pcie->parf + PARF_ECAM_BASE_HI);
> +
> +	/*
> +	 * The only device on root bus is the Root Port. Any access other than that
> +	 * should not go out of the link and should return all F's. Since the iATU
> +	 * is configured for the buses which starts after root bus, block the transactions
> +	 * starting from function 1 of the root bus to the end of the root bus (i.e from
> +	 * dbi_base + 4kb to dbi_base + 1MB) from going outside the link.

99% of this file fits in 80 columns.  Wrap comments to do the same.

The text doesn't quite make sense because accesses to devices on the
root bus *never* involve a link.  Only Root Ports have links and the
links all lead to buses other than the root bus.