linux-kernel - Re: [PATCH v5 03/16] CXL/PCI: Introduce PCIe helper functions pcie_is_cxl() and pcie_is_cxl

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Message-ID: <6785a691b56f2_186d9b2942@iweiny-mobl.notmuch>
Date: Mon, 13 Jan 2025 17:49:37 -0600
From: Ira Weiny <ira.weiny@...el.com>
To: Terry Bowman <terry.bowman@....com>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<nifan.cxl@...il.com>, <dave@...olabs.net>, <jonathan.cameron@...wei.com>,
	<dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<vishal.l.verma@...el.com>, <dan.j.williams@...el.com>,
	<bhelgaas@...gle.com>, <mahesh@...ux.ibm.com>, <ira.weiny@...el.com>,
	<oohall@...il.com>, <Benjamin.Cheatham@....com>, <rrichter@....com>,
	<nathan.fontenot@....com>, <Smita.KoralahalliChannabasappa@....com>,
	<lukas@...ner.de>, <ming.li@...omail.com>,
	<PradeepVineshReddy.Kodamati@....com>, <alucerop@....com>
Subject: Re: [PATCH v5 03/16] CXL/PCI: Introduce PCIe helper functions
 pcie_is_cxl() and pcie_is_cxl_port()

Terry Bowman wrote:
> CXL and AER drivers need the ability to identify CXL devices and CXL port
> devices.
> 
> First, add set_pcie_cxl() with logic checking for CXL Flexbus DVSEC
> presence. The CXL Flexbus DVSEC presence is used because it is required
> for all the CXL PCIe devices.[1]
> 
> Add boolean 'struct pci_dev::is_cxl' with the purpose to cache the CXL
> Flexbus presence.
> 
> Add pcie_is_cxl() as a macro to return 'struct pci_dev::is_cxl'.
> 
> Add pcie_is_cxl_port() to check if a device is a CXL Root Port, CXL
> Upstream Switch Port, or CXL Downstream Switch Port. Also, verify the
> CXL Extensions DVSEC for Ports is present.[1]
> 
> [1] CXL 3.1 Spec, 8.1.1 PCIe Designated Vendor-Specific Extended
>     Capability (DVSEC) ID Assignment, Table 8-2
> 
> Signed-off-by: Terry Bowman <terry.bowman@....com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> Reviewed-by: Fan Ni <fan.ni@...sung.com>
> ---
>  drivers/pci/pci.c             | 13 +++++++++++++
>  drivers/pci/probe.c           | 10 ++++++++++
>  include/linux/pci.h           |  4 ++++
>  include/uapi/linux/pci_regs.h |  3 ++-
>  4 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 661f98c6c63a..9319c62e3488 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5036,10 +5036,23 @@ static int pci_dev_reset_slot_function(struct pci_dev *dev, bool probe)
>  
>  static u16 cxl_port_dvsec(struct pci_dev *dev)
>  {
> +	if (!pcie_is_cxl(dev))
> +		return 0;
> +
>  	return pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
>  					 PCI_DVSEC_CXL_PORT);
>  }
>  
> +bool pcie_is_cxl_port(struct pci_dev *dev)
> +{
> +	if ((pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT) &&
> +	    (pci_pcie_type(dev) != PCI_EXP_TYPE_UPSTREAM) &&
> +	    (pci_pcie_type(dev) != PCI_EXP_TYPE_DOWNSTREAM))
> +		return false;
> +
> +	return cxl_port_dvsec(dev);

Returning bool from a function which returns u16 is odd and I don't think
it should be coded this way.  I don't think it is wrong right now but this
really ought to code the pcie_is_cxl() here and leave cxl_port_dvsec()
alone.  Calling cxl_port_dvsec(), checking for if the dvsec exists, and
returning bool.

> +}
> +

[snip]

> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index e2e36f11205c..08350302b3e9 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -452,6 +452,7 @@ struct pci_dev {
>  	unsigned int	is_hotplug_bridge:1;
>  	unsigned int	shpc_managed:1;		/* SHPC owned by shpchp */
>  	unsigned int	is_thunderbolt:1;	/* Thunderbolt controller */
> +	unsigned int	is_cxl:1;               /* Compute Express Link (CXL) */
>  	/*
>  	 * Devices marked being untrusted are the ones that can potentially
>  	 * execute DMA attacks and similar. They are typically connected
> @@ -739,6 +740,9 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
>  	return false;
>  }
>  
> +#define pcie_is_cxl(dev) (dev->is_cxl)

This should be an inline function which takes struct pci_dev * for type
safety.

Ira

[snip]