linux-kernel - Re: [PATCH v12 06/13] PCI: dwc: Add dw_pcie_parent_bus

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Message-ID: <Z+GlWm4QAkuyb9nI@lizhi-Precision-Tower-5810>
Date: Mon, 24 Mar 2025 14:32:58 -0400
From: Frank Li <Frank.li@....com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Bjorn Helgaas <helgaas@...nel.org>, Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Niklas Cassel <cassel@...nel.org>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v12 06/13] PCI: dwc: Add dw_pcie_parent_bus_offset()
 checking and debug

On Mon, Mar 24, 2025 at 11:00:24PM +0530, Manivannan Sadhasivam wrote:
> On Sat, Mar 15, 2025 at 03:15:41PM -0500, Bjorn Helgaas wrote:
> > From: Frank Li <Frank.Li@....com>
> >
> > dw_pcie_parent_bus_offset() looks up the parent bus address of a PCI
> > controller 'reg' property in devicetree.  If implemented, .cpu_addr_fixup()
> > is a hard-coded way to get the parent bus address corresponding to a CPU
> > physical address.
> >
> > Add debug code to compare the address from .cpu_addr_fixup() with the
> > address from devicetree.  If they match, warn that .cpu_addr_fixup() is
> > redundant and should be removed; if they differ, warn that something is
> > wrong with the devicetree.
> >
> > If .cpu_addr_fixup() is not implemented, the parent bus address should be
> > identical to the CPU physical address because we previously ignored the
> > parent bus address from devicetree.  If the devicetree has a different
> > parent bus address, warn about it being broken.
> >
> > [bhelgaas: split debug to separate patch for easier future revert, commit
> > log]
> > Link: https://lore.kernel.org/r/20250313-pci_fixup_addr-v11-5-01d2313502ab@nxp.com
> > Signed-off-by: Frank Li <Frank.Li@....com>
> > Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware.c | 26 +++++++++++++++++++-
> >  drivers/pci/controller/dwc/pcie-designware.h | 13 ++++++++++
> >  2 files changed, 38 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > index 0a35e36da703..985264c88b92 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -1114,7 +1114,8 @@ resource_size_t dw_pcie_parent_bus_offset(struct dw_pcie *pci,
> >  	struct device *dev = pci->dev;
> >  	struct device_node *np = dev->of_node;
> >  	int index;
> > -	u64 reg_addr;
> > +	u64 reg_addr, fixup_addr;
> > +	u64 (*fixup)(struct dw_pcie *pcie, u64 cpu_addr);
> >
> >  	/* Look up reg_name address on parent bus */
> >  	index = of_property_match_string(np, "reg-names", reg_name);
> > @@ -1126,5 +1127,28 @@ resource_size_t dw_pcie_parent_bus_offset(struct dw_pcie *pci,
> >
> >  	of_property_read_reg(np, index, &reg_addr, NULL);
> >
> > +	fixup = pci->ops->cpu_addr_fixup;
> > +	if (fixup) {
> > +		fixup_addr = fixup(pci, cpu_phy_addr);
> > +		if (reg_addr == fixup_addr) {
> > +			dev_warn(dev, "%#010llx %s reg[%d] == %#010llx; %ps is redundant\n",
> > +				 cpu_phy_addr, reg_name, index,
> > +				 fixup_addr, fixup);
> > +		} else {
> > +			dev_warn(dev, "%#010llx %s reg[%d] != %#010llx fixed up addr; devicetree is broken\n",
> > +				 cpu_phy_addr, reg_name,
> > +				 index, fixup_addr);
> > +			reg_addr = fixup_addr;
> > +		}
> > +	} else if (!pci->use_parent_dt_ranges) {
>
> Is this check still valid? 'use_parent_dt_ranges' is only used here for
> validation. Moreover, if the fixup is not available, we should be able to
> safely return 'cpu_phy_addr - reg_addr' unconditionally.

I worry about some platform use fake bus address translation in dtb file.
If none report below warn for some times, we can remove all
use_parent_dt_ranges.

Frank

>
> > +		if (reg_addr != cpu_phy_addr) {
> > +			dev_warn(dev, "devicetree has incorrect translation; please check parent \"ranges\" property. CPU physical addr %#010llx, parent bus addr %#010llx\n",
> > +				 cpu_phy_addr, reg_addr);
> > +			return 0;
> > +		}
> > +	}
> > +
> > +	dev_info(dev, "%s parent bus offset is %#010llx\n",
> > +		 reg_name, cpu_phy_addr - reg_addr);
>
> This info is useless on platforms having no translation between CPU and PCI
> controller. The offset will always be 0.
>
> - Mani
>
> --
> மணிவண்ணன் சதாசிவம்