linux-kernel - Re: [PATCH v6 5/5] PCI: qcom: Add support for ECAM feature

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Message-ID: <75cab14e-e57d-4d1f-aaf2-ca75dd37154f@oss.qualcomm.com>
Date: Mon, 14 Jul 2025 12:38:22 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
        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>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, Jingoo Han <jingoohan1@...il.com>
Cc: 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 v6 5/5] PCI: qcom: Add support for ECAM feature

On 7/12/25 1:42 AM, 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 override ELBI with the
> offset from PARF_SLV_DBI_ELBI and cfg win to map these regions.
> 
> On root bus, we have only 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 through ECAM blocker through PARF registers.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---

[...]

> +	if (pp->ecam_mode) {
> +		/*
> +		 * Override ELBI in ecam mode, as in ecam mode
> +		 * ELBI moves along with the dbi config space.
> +		 */
> +		offset = readl(pcie->parf + PARF_SLV_DBI_ELBI);

I see that the offset is supposed to take up 12 lower bits with the
remaining ones being reserved. Out of abundance of caution, please
add a #define SLV_DBI_ELBI_ADDR_BASE GENMASK(11, 0) and FIELD_GET it

no concerns apart from that, I think

Konrad