linux-kernel - Re: [RFC PATCH 1/9] cxl/acpi: Add an acpi

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Date:   Wed, 11 Nov 2020 07:10:06 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Ben Widawsky <ben.widawsky@...el.com>
Cc:     linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH 1/9] cxl/acpi: Add an acpi_cxl module for the CXL
 interconnect

On Tue, Nov 10, 2020 at 09:43:48PM -0800, Ben Widawsky wrote:
> +menuconfig CXL_BUS
> +	tristate "CXL (Compute Express Link) Devices Support"
> +	help
> +	  CXL is a bus that is electrically compatible with PCI-E, but layers
> +	  three protocols on that signalling (CXL.io, CXL.cache, and CXL.mem). The
> +	  CXL.cache protocol allows devices to hold cachelines locally, the
> +	  CXL.mem protocol allows devices to be fully coherent memory targets, the
> +	  CXL.io protocol is equivalent to PCI-E. Say 'y' to enable support for
> +	  the configuration and management of devices supporting these protocols.
> +

Please fix the overly long lines.

> +static void acpi_cxl_desc_init(struct acpi_cxl_desc *acpi_desc, struct device *dev)


Another overly long line.

> +{
> +	dev_set_drvdata(dev, acpi_desc);
> +	acpi_desc->dev = dev;
> +}

But this helper seems pretty pointless to start with.

> +static int acpi_cxl_remove(struct acpi_device *adev)
> +{
> +	return 0;
> +}

The emptry remove callback is not needed.

> +/*
> + * If/when CXL support is defined by other platform firmware the kernel
> + * will need a mechanism to select between the platform specific version
> + * of this routine, until then, hard-code ACPI assumptions
> + */
> +int cxl_bus_prepared(struct pci_dev *pdev)
> +{
> +	struct acpi_device *adev;
> +	struct pci_dev *root_port;
> +	struct device *root;
> +
> +	root_port = pcie_find_root_port(pdev);
> +	if (!root_port)
> +		return -ENXIO;
> +
> +	root = root_port->dev.parent;
> +	if (!root)
> +		return -ENXIO;
> +
> +	adev = ACPI_COMPANION(root);
> +	if (!adev)
> +		return -ENXIO;
> +
> +	/* TODO: OSC enabling */
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(cxl_bus_prepared);

What is the point of this function?  I doesn't realy do anything,
not even a CXL specific check.  

>  
> +/*******************************************************************************
> + *
> + * CEDT - CXL Early Discovery Table (ACPI 6.4)
> + *        Version 1
> + *
> + ******************************************************************************/
> +

Pleae use the normal Linux comment style.


> +#define ACPI_CEDT_CHBS_VERSION_CXL11    (0)
> +#define ACPI_CEDT_CHBS_VERSION_CXL20    (1)
> +
> +/* Values for length field above */
> +
> +#define ACPI_CEDT_CHBS_LENGTH_CXL11     (0x2000)
> +#define ACPI_CEDT_CHBS_LENGTH_CXL20     (0x10000)

No need for the braces.