linux-kernel - Re: [PATCH v10 02/17] PCI/CXL: Add pcie_is

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Message-ID: <6881626a784f_134cc7100b4@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 23 Jul 2025 15:30:02 -0700
From: <dan.j.williams@...el.com>
To: Terry Bowman <terry.bowman@....com>, <dave@...olabs.net>,
	<jonathan.cameron@...wei.com>, <dave.jiang@...el.com>,
	<alison.schofield@...el.com>, <dan.j.williams@...el.com>,
	<bhelgaas@...gle.com>, <shiju.jose@...wei.com>, <ming.li@...omail.com>,
	<Smita.KoralahalliChannabasappa@....com>, <rrichter@....com>,
	<dan.carpenter@...aro.org>, <PradeepVineshReddy.Kodamati@....com>,
	<lukas@...ner.de>, <Benjamin.Cheatham@....com>,
	<sathyanarayanan.kuppuswamy@...ux.intel.com>, <terry.bowman@....com>,
	<linux-cxl@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v10 02/17] PCI/CXL: Add pcie_is_cxl()

Terry Bowman wrote:
> CXL and AER drivers need the ability to identify CXL devices.
> 
> 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 function pcie_is_cxl() to return 'struct pci_dev::is_cxl'.
> 
> [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: Ira Weiny <ira.weiny@...el.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
>  drivers/pci/probe.c           | 10 ++++++++++
>  include/linux/pci.h           |  6 ++++++
>  include/uapi/linux/pci_regs.h |  8 +++++++-
>  3 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 4b8693ec9e4c..5d3548648d5c 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1691,6 +1691,14 @@ static void set_pcie_thunderbolt(struct pci_dev *dev)
>  		dev->is_thunderbolt = 1;
>  }
>  
> +static void set_pcie_cxl(struct pci_dev *dev)
> +{
> +	u16 dvsec = pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
> +					      PCI_DVSEC_CXL_FLEXBUS);
> +	if (dvsec)
> +		dev->is_cxl = 1;
> +}
> +
>  static void set_pcie_untrusted(struct pci_dev *dev)
>  {
>  	struct pci_dev *parent = pci_upstream_bridge(dev);
> @@ -2021,6 +2029,8 @@ int pci_setup_device(struct pci_dev *dev)
>  	/* Need to have dev->cfg_size ready */
>  	set_pcie_thunderbolt(dev);
>  
> +	set_pcie_cxl(dev);

Per the comment in the header below, in the case of upstream ports and
endpoints, this should walk to the parent downstream port and make sure
the cxl setting matches. I.e. with hotplug the downstream port may
transition from not-cxl to is-cxl. Update downstream-port parents at the
beginning of life of their CXL child-devices.

> +
>  	set_pcie_untrusted(dev);
>  
>  	if (pci_is_pcie(dev))
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 05e68f35f392..79878243b681 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -453,6 +453,7 @@ 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
> @@ -744,6 +745,11 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
>  	return false;
>  }
>  
> +static inline bool pcie_is_cxl(struct pci_dev *pci_dev)
> +{
> +	return pci_dev->is_cxl;
> +}
> +
>  #define for_each_pci_bridge(dev, bus)				\
>  	list_for_each_entry(dev, &bus->devices, bus_list)	\
>  		if (!pci_is_bridge(dev)) {} else
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index a3a3e942dedf..fb9d77c69d5f 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -1225,9 +1225,15 @@
>  /* Deprecated old name, replaced with PCI_DOE_DATA_OBJECT_DISC_RSP_3_TYPE */
>  #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL		PCI_DOE_DATA_OBJECT_DISC_RSP_3_TYPE
>  
> -/* Compute Express Link (CXL r3.1, sec 8.1.5) */
> +/* Compute Express Link (CXL r3.2, sec 8.1)
> + *
> + * Note that CXL DVSEC id 3 and 7 to be ignored when the CXL link state
> + * is "disconnected" (CXL r3.2, sec 9.12.3). Re-enumerate these
> + * registers on downstream link-up events.
> + */
>  #define PCI_DVSEC_CXL_PORT				3
>  #define PCI_DVSEC_CXL_PORT_CTL				0x0c
>  #define PCI_DVSEC_CXL_PORT_CTL_UNMASK_SBR		0x00000001
> +#define PCI_DVSEC_CXL_FLEXBUS				7

Please, let us not end up with multiple definitions for the same thing
in multiple places. I note that Alejandro introduces include/cxl/pci.h
with some of the CXL DVSEC definitions from drivers/cxl/cxlpci.h.
Although not all of them, I think a precursor patch to move all of them
in this patch set is the way to go. I.e. drop all these PCI_DVSEC_CXL_*
versions in favor of their existing CXL_DVSEC_* versions.