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Message-ID: <20250905190840.GA1318549@bhelgaas>
Date: Fri, 5 Sep 2025 14:08:40 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: 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>,
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 10:08:54PM +0530, Manivannan Sadhasivam wrote:
> On Fri, Sep 05, 2025 at 10:47:42AM GMT, 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.
> > > >
> > > > Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> > > > ---
> > > > drivers/pci/controller/dwc/pcie-qcom.c | 70 ++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 70 insertions(+)
> > > >
> > > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > > index 5092752de23866ef95036bb3f8fae9bb06e8ea1e..8f3c86c77e2604fd7826083f63b66b4cb62a341d 100644
> > > > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > > > @@ -55,6 +55,7 @@
> > > > #define PARF_AXI_MSTR_WR_ADDR_HALT_V2 0x1a8
> > > > #define PARF_Q2A_FLUSH 0x1ac
> > > > #define PARF_LTSSM 0x1b0
> > > > +#define PARF_SLV_DBI_ELBI 0x1b4
> > > > #define PARF_INT_ALL_STATUS 0x224
> > > > #define PARF_INT_ALL_CLEAR 0x228
> > > > #define PARF_INT_ALL_MASK 0x22c
> > > > @@ -64,6 +65,16 @@
> > > > #define PARF_DBI_BASE_ADDR_V2_HI 0x354
> > > > #define PARF_SLV_ADDR_SPACE_SIZE_V2 0x358
> > > > #define PARF_SLV_ADDR_SPACE_SIZE_V2_HI 0x35c
> > > > +#define PARF_BLOCK_SLV_AXI_WR_BASE 0x360
> > > > +#define PARF_BLOCK_SLV_AXI_WR_BASE_HI 0x364
> > > > +#define PARF_BLOCK_SLV_AXI_WR_LIMIT 0x368
> > > > +#define PARF_BLOCK_SLV_AXI_WR_LIMIT_HI 0x36c
> > > > +#define PARF_BLOCK_SLV_AXI_RD_BASE 0x370
> > > > +#define PARF_BLOCK_SLV_AXI_RD_BASE_HI 0x374
> > > > +#define PARF_BLOCK_SLV_AXI_RD_LIMIT 0x378
> > > > +#define PARF_BLOCK_SLV_AXI_RD_LIMIT_HI 0x37c
> > > > +#define PARF_ECAM_BASE 0x380
> > > > +#define PARF_ECAM_BASE_HI 0x384
> > > > #define PARF_NO_SNOOP_OVERRIDE 0x3d4
> > > > #define PARF_ATU_BASE_ADDR 0x634
> > > > #define PARF_ATU_BASE_ADDR_HI 0x638
> > > > @@ -87,6 +98,7 @@
> > > > /* PARF_SYS_CTRL register fields */
> > > > #define MAC_PHY_POWERDOWN_IN_P2_D_MUX_EN BIT(29)
> > > > +#define PCIE_ECAM_BLOCKER_EN BIT(26)
> > > > #define MST_WAKEUP_EN BIT(13)
> > > > #define SLV_WAKEUP_EN BIT(12)
> > > > #define MSTR_ACLK_CGC_DIS BIT(10)
> > > > @@ -134,6 +146,9 @@
> > > > /* PARF_LTSSM register fields */
> > > > #define LTSSM_EN BIT(8)
> > > > +/* PARF_SLV_DBI_ELBI */
> > > > +#define SLV_DBI_ELBI_ADDR_BASE GENMASK(11, 0)
> > > > +
> > > > /* PARF_INT_ALL_{STATUS/CLEAR/MASK} register fields */
> > > > #define PARF_INT_ALL_LINK_UP BIT(13)
> > > > #define PARF_INT_MSI_DEV_0_7 GENMASK(30, 23)
> > > > @@ -317,6 +332,48 @@ static void qcom_ep_reset_deassert(struct qcom_pcie *pcie)
> > > > qcom_perst_assert(pcie, false);
> > > > }
> > > > +static void qcom_pci_config_ecam(struct dw_pcie_rp *pp)
> > > > +{
> > > > + struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> > > > + struct qcom_pcie *pcie = to_qcom_pcie(pci);
> > > > + u64 addr, addr_end;
> > > > + u32 val;
> > > > +
> > > > + /* 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 to the PCIe
> > > > + * region will go outside the PCIe link. As part of enumeration the PCI
> > > > + * sw can try to read to vendor ID & device ID with different device
> > > > + * number and function number under root bus. As any access other than
> > > > + * root bus, device 0, function 0, 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.
> > > > + */
> > > > + addr = pci->dbi_phys_addr + SZ_4K;
> > > > + writel_relaxed(lower_32_bits(addr), pcie->parf + PARF_BLOCK_SLV_AXI_WR_BASE);
> > > > + writel_relaxed(upper_32_bits(addr), pcie->parf + PARF_BLOCK_SLV_AXI_WR_BASE_HI);
> > > > +
> > > > + writel_relaxed(lower_32_bits(addr), pcie->parf + PARF_BLOCK_SLV_AXI_RD_BASE);
> > > > + writel_relaxed(upper_32_bits(addr), pcie->parf + PARF_BLOCK_SLV_AXI_RD_BASE_HI);
> > > > +
> > > > + addr_end = pci->dbi_phys_addr + SZ_1M - 1;
> > > > +
> > > > + writel_relaxed(lower_32_bits(addr_end), pcie->parf + PARF_BLOCK_SLV_AXI_WR_LIMIT);
> > > > + writel_relaxed(upper_32_bits(addr_end), pcie->parf + PARF_BLOCK_SLV_AXI_WR_LIMIT_HI);
> > > > +
> > > > + writel_relaxed(lower_32_bits(addr_end), pcie->parf + PARF_BLOCK_SLV_AXI_RD_LIMIT);
> > > > + writel_relaxed(upper_32_bits(addr_end), pcie->parf + PARF_BLOCK_SLV_AXI_RD_LIMIT_HI);
> > > > +
> > > > + val = readl_relaxed(pcie->parf + PARF_SYS_CTRL);
> > > > + val |= PCIE_ECAM_BLOCKER_EN;
> > > > + writel_relaxed(val, pcie->parf + PARF_SYS_CTRL);
> > > > +}
> > > > +
> > > > static int qcom_pcie_start_link(struct dw_pcie *pci)
> > > > {
> > > > struct qcom_pcie *pcie = to_qcom_pcie(pci);
> > > > @@ -326,6 +383,9 @@ static int qcom_pcie_start_link(struct dw_pcie *pci)
> > > > qcom_pcie_common_set_16gt_lane_margining(pci);
> > > > }
> > > > + if (pci->pp.ecam_enabled)
> > > > + qcom_pci_config_ecam(&pci->pp);
> > > > +
> > > > /* Enable Link Training state machine */
> > > > if (pcie->cfg->ops->ltssm_enable)
> > > > pcie->cfg->ops->ltssm_enable(pcie);
> > > > @@ -1314,6 +1374,7 @@ static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
> > > > {
> > > > struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> > > > struct qcom_pcie *pcie = to_qcom_pcie(pci);
> > > > + u16 offset;
> > > > int ret;
> > > > qcom_ep_reset_assert(pcie);
> > > > @@ -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.
>
> Theoretically there is a hole, but practically there isn't. ELBI
> register is only used by legacy Qcom SoCs and they do not support
> ECAM. So they will continue to use the valid ELBI register region
> from DT.
That's a real pain to figure out from code analysis, so I would prefer
to squash them to avoid even the appearance of 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.
>
> Though there is no practical issue, it still makes sense to set
> 'elbi_base' to a valid region before enabling ECAM.
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