linux-kernel - Re: [PATCH v8 5/5] PCI: qcom: Add support for ECAM feature

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Message-ID: <20250905152608.GA1305931@bhelgaas>
Date: Fri, 5 Sep 2025 10:26:08 -0500
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>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.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 v8 5/5] PCI: qcom: Add support for ECAM feature

On Fri, Sep 05, 2025 at 10:47:42AM +0530, Krishna Chaitanya Chundru wrote:
> On 9/4/2025 1:42 AM, Bjorn Helgaas wrote:
> > On Thu, Aug 28, 2025 at 01:04:26PM +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 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.

> > > @@ -1322,6 +1383,15 @@ static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
> > >   	if (ret)
> > >   		return ret;
> > > +	if (pp->ecam_enabled) {
> > > +		/*
> > > +		 * Override ELBI when ECAM is enabled, as when ECAM
> > > +		 * is enabled ELBI moves along with the dbi config space.
> > > +		 */
> > > +		offset = FIELD_GET(SLV_DBI_ELBI_ADDR_BASE, readl(pcie->parf + PARF_SLV_DBI_ELBI));
> > > +		pci->elbi_base = pci->dbi_base + offset;
> > 
> > This looks like there might be a bisection hole between this patch and
> > the previous patch that enables ECAM in the DWC core?  Obviously I
> > would want to avoid a bisection hole.
> > 
> > What happens to qcom ELBI accesses between these two patches?  It
> > looks like they would go to the wrong address until this elbi_base
> > update.

> > Is this connection between DBI and ELBI specific to qcom, or might
> > other users of ELBI (only exynos, I guess) need a similar update to
> > elbi_base?
> > 
> This is specific to QCOM only, with the commit 10ba0854c5e61 ("PCI:
> qcom: Disable mirroring of DBI and iATU register space in BAR region")
> The DBI address can moved to upper region of the PCIe region. When DBI
> is moved ELBI also moves along with it. So if this patch is not present
> elbi will not point to correct ELBI address.

So I think you're saying this [5/5] patch should be squashed into the
[4/5] patch that changes the way pci->dbi_base is computed?

After [4/5], pcie-qcom.c still uses pci->elbi_base, but apparently the
value is wrong until this update in [5/5]?

Bjorn