linux-kernel - Re: [PATCH v9 3/4] PCI: qcom: Prepare for the DWC ECAM enablement

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Message-ID: <20250912215053.GA1643809@bhelgaas>
Date: Fri, 12 Sep 2025 16:50:53 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Jingoo Han <jingoohan1@...il.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Jonathan Chocron <jonnyc@...zon.com>, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Subject: Re: [PATCH v9 3/4] PCI: qcom: Prepare for the DWC ECAM enablement

On Tue, Sep 09, 2025 at 12:37:52PM +0530, Manivannan Sadhasivam wrote:
> From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> 
> To support the DWC ECAM mechanism, prepare the driver by performing below
> configurations:
> 
>   1. Since the ELBI region will be covered by the ECAM 'config' space,
>      override the 'elbi_base' with the address derived from 'dbi_base' and
>      the offset from PARF_SLV_DBI_ELBI register.
> 
>   2. Block the transactions from the host bridge to devices other than Root
>      Port on the root bus to return all F's. This is required when the 'CFG
>      Shift Feature' of iATU is enabled.

FWIW, before I noticed your v9, I had updated the comments here to fix
a few inconsistencies.  Here's the diff:

diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
index 7c2b2c8c61c2..962f0311a23a 100644
--- a/drivers/pci/controller/dwc/pcie-qcom.c
+++ b/drivers/pci/controller/dwc/pcie-qcom.c
@@ -343,15 +343,15 @@ static void qcom_pci_config_ecam(struct dw_pcie_rp *pp)
 	writel_relaxed(upper_32_bits(pci->dbi_phys_addr), pcie->parf + PARF_ECAM_BASE_HI);
 
 	/*
-	 * The only device on root bus is a single Root Port. So if PCI core
-	 * tries to access any devices other than Device/Function (0.0) in Bus
-	 * 0, the TLP will go outside of the controller to the PCI bus. But with
-	 * CFG Shift Feature (ECAM) enabled in iATU, there is no guarantee that
-	 * the response is going to be all F's. Hence, to make sure that the
+	 * The only device on the root bus is a single Root Port. If we try to
+	 * access any devices other than Device/Function 00.0 on Bus 0, the TLP
+	 * will go outside of the controller to the PCI bus. But with CFG Shift
+	 * Feature (ECAM) enabled in iATU, there is no guarantee that the
+	 * response is going to be all F's. Hence, to make sure that the
 	 * requester gets all F's response for accesses other than the Root
-	 * Port, configure iATU to 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).
+	 * Port, configure iATU to 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).
 	 */
 	addr = pci->dbi_phys_addr + SZ_4K;
 	writel_relaxed(lower_32_bits(addr), pcie->parf + PARF_BLOCK_SLV_AXI_WR_BASE);
@@ -1385,7 +1385,7 @@ static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
 	if (pp->ecam_enabled) {
 		/*
 		 * Override ELBI when ECAM is enabled, as when ECAM
-		 * is enabled ELBI moves along with the dbi config space.
+		 * 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;