Re: [PATCH v9 05/16] PCI: imx6: Using "linux,pci-domain" as slot ID

From: Bjorn Helgaas <helgaas@kernel.org>
To: Frank Li <Frank.Li@nxp.com>
Cc: manivannan.sadhasivam@linaro.org, bhelgaas@google.com,
	conor+dt@kernel.org, devicetree@vger.kernel.org,
	festevam@gmail.com, hongxing.zhu@nxp.com, imx@lists.linux.dev,
	kernel@pengutronix.de, krzysztof.kozlowski+dt@linaro.org,
	krzysztof.kozlowski@linaro.org, kw@linux.com,
	l.stach@pengutronix.de, linux-arm-kernel@lists.infradead.org,
	linux-imx@nxp.com, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org, lpieralisi@kernel.org,
	robh@kernel.org, s.hauer@pengutronix.de, shawnguo@kernel.org
Subject: Re: [PATCH v9 05/16] PCI: imx6: Using "linux,pci-domain" as slot ID
Date: Fri, 2 Feb 2024 15:54:31 -0600	[thread overview]
Message-ID: <20240202215431.GA728556@bhelgaas> (raw)
In-Reply-To: <20240119171122.3057511-6-Frank.Li@nxp.com>

On Fri, Jan 19, 2024 at 12:11:11PM -0500, Frank Li wrote:
> Avoid use get slot id by compared with register physical address. If there
> are more than 2 slots, compared logic will become complex.
> 
> "linux,pci-domain" already exist at dts since commit:
> 	commit (c0b70f05c87f3b arm64: dts: imx8mq: use_dt_domains for pci node).
> 
> So it is safe to remove compare basic address code:
> 	...
> 	if (dbi_base->start == IMX8MQ_PCIE2_BASE_ADDR)
> 		imx6_pcie->controller_id = 1;
> 	...

I have no idea what this is telling me.  I guess you don't want to use
IMX8MQ_PCIE2_BASE_ADDR to decide something?  That much sounds good:
the *address* of some MMIO space doesn't tell us anything about the
function of that space.

I expect the "compatible" string to tell the driver what the
programming model of the device is.

> +	/* Using linux,pci-domain as PCI slot id */
> +	imx6_pcie->controller_id = of_get_pci_domain_nr(node);
> +	/*
> +	 * If there are no "linux,pci-domain" property specified in DT, then assume only one
> +	 * controller is available.
> +	 */
> +	if (imx6_pcie->controller_id == -EINVAL)
> +		imx6_pcie->controller_id = 0;
> +	else if (imx6_pcie->controller_id < 0)
> +		return dev_err_probe(dev, imx6_pcie->controller_id,
> +				     "linux,pci-domain have wrong value\n");

Maybe I'm missing something here.  It looks like this driver uses
controller_id to distinguish between hardware variants or maybe
between two Root Ports (slots?) in the same SoC?

  imx6_pcie_grp_offset
    return imx6_pcie->controller_id == 1 ? IOMUXC_GPR16 : IOMUXC_GPR14;

  imx6_pcie_configure_type
    id = imx6_pcie->controller_id
    if (!drvdata->mode_mask[id])         # <-- looks unsafe
      id = 0;
    regmap_update_bits(drvdata->mode_off[id], ...)

(This "mode_mask[id]" looks like it will reference garbage if the DT
supplies "linux,pci-domain = <2>".  A bogus DT shouldn't be able to
cause a driver to misbehave like that.)

That doesn't seem related to "linux,pci-domain" at all.

Bjorn