linux-kernel - Re: [PATCH v2 03/14] cxl/pci: Introduce helper functions pcie_is_cxl() and pcie_is_cxl

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Message-ID: <a68f58d4-d79d-4c91-855f-9bfb36013cc4@intel.com>
Date: Thu, 31 Oct 2024 09:25:41 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Terry Bowman <terry.bowman@....com>, ming4.li@...el.com,
 linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-pci@...r.kernel.org, dave@...olabs.net, jonathan.cameron@...wei.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
Subject: Re: [PATCH v2 03/14] cxl/pci: Introduce helper functions
 pcie_is_cxl() and pcie_is_cxl_port()



On 10/25/24 2:02 PM, 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 port 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: Dave Jiang <dave.jiang@...el.com>
> ---
>  drivers/pci/pci.c             | 14 ++++++++++++++
>  drivers/pci/probe.c           | 10 ++++++++++
>  include/linux/pci.h           |  4 ++++
>  include/uapi/linux/pci_regs.h |  3 ++-
>  4 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7d85c04fbba2..c1b243aec61c 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5034,6 +5034,20 @@ static u16 cxl_port_dvsec(struct pci_dev *dev)
>  					 PCI_DVSEC_CXL_PORT);
>  }
>  
> +bool pcie_is_cxl_port(struct pci_dev *dev)
> +{
> +	if (!pcie_is_cxl(dev))
> +		return false;
> +
> +	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);
> +}
> +EXPORT_SYMBOL_GPL(pcie_is_cxl_port);
> +
>  static bool cxl_sbr_masked(struct pci_dev *dev)
>  {
>  	u16 dvsec, reg;
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 4f68414c3086..9324eb345f11 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1631,6 +1631,14 @@ 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;
> @@ -1945,6 +1953,8 @@ int pci_setup_device(struct pci_dev *dev)
>  	/* Need to have dev->cfg_size ready */
>  	set_pcie_thunderbolt(dev);
>  
> +	set_pcie_cxl(dev);
> +
>  	set_pcie_untrusted(dev);
>  
>  	/* "Unknown power state" */
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 106ac83e3a7b..d3b1af9fb273 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -443,6 +443,7 @@ 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;               /* CXL alternate protocol */
>  	/*
>  	 * Devices marked being untrusted are the ones that can potentially
>  	 * execute DMA attacks and similar. They are typically connected
> @@ -743,6 +744,9 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
>  	return false;
>  }
>  
> +#define pcie_is_cxl(dev) (dev->is_cxl)
> +bool pcie_is_cxl_port(struct pci_dev *dev);
> +
>  #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 12323b3334a9..5df6c74963c5 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -1186,9 +1186,10 @@
>  #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_PROTOCOL		0x00ff0000
>  #define PCI_DOE_DATA_OBJECT_DISC_RSP_3_NEXT_INDEX	0xff000000
>  
> -/* Compute Express Link (CXL r3.1, sec 8.1.5) */
> +/* Compute Express Link (CXL r3.1, sec 8.1) */
>  #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
>  
>  #endif /* LINUX_PCI_REGS_H */