linux-kernel - Re: [PATCH v12 05/13] PCI: dwc: Add dw_pcie_parent_bus

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Message-ID: <20250324182827.GA1257218@bhelgaas>
Date: Mon, 24 Mar 2025 13:28:27 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Frank Li <Frank.Li@....com>, 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 05/13] PCI: dwc: Add dw_pcie_parent_bus_offset()

On Mon, Mar 24, 2025 at 10:48:23PM +0530, Manivannan Sadhasivam wrote:
> On Sat, Mar 15, 2025 at 03:15:40PM -0500, Bjorn Helgaas wrote:
> > From: Frank Li <Frank.Li@....com>
> > 
> > Return the offset from CPU physical address to the parent bus address of
> > the specified element of the devicetree 'reg' property.

> > +resource_size_t dw_pcie_parent_bus_offset(struct dw_pcie *pci,
> > +					  const char *reg_name,
> > +					  resource_size_t cpu_phy_addr)
> > +{
> 
> s/cpu_phy_addr/cpu_phys_addr/g

Fixed, thanks!

> > +	struct device *dev = pci->dev;
> > +	struct device_node *np = dev->of_node;
> > +	int index;
> > +	u64 reg_addr;
> > +
> > +	/* Look up reg_name address on parent bus */
> 
> 'parent bus' is not accurate as the below code checks for the 'reg_name' in
> current PCI controller node.

We want the address of "reg_name" on the node's primary side.  We've
been calling that the "parent bus address", I guess because it's the
address on the "parent bus" of the node.

I'm not sure what the best term is for this.  Do you have a
suggestion?

If "parent bus address" is the wrong term, maybe we need to rename
dw_pcie_parent_bus_offset() itself?  

Currently we pass in cpu_phys_addr, but this function doesn't need it
except for the debug code added later.  I would really rather have
something like this in the callers:

  pci->parent_bus_offset = pp->cfg0_base -
      dw_pcie_parent_bus_addr(pci, "config");

because then the offset is computed sort of at the same level where
it's used, and a grep for "cfg0_base" would find both the set and the
use and they would be easy to match up.

> > +	index = of_property_match_string(np, "reg-names", reg_name);
> > +
> > +	if (index < 0) {
> > +		dev_err(dev, "No %s in devicetree \"reg\" property\n", reg_name);
> 
> Both of these callers are checking for the existence of the
> 'reg_name' property before calling this API. So this check seems to
> be redundant (for now).

True, but I don't see a way to enforce the caller checks.  I don't
like the idea of calling of_property_read_reg(np, index, ...) where we
have to look the caller to verify that "index" is valid.

Bjorn