linux-kernel - Re: [PATCH v7 03/17] CXL/PCI: Introduce PCIe helper functions pcie_is_cxl() and pcie_is_cxl

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Message-ID: <91dbfcd7-8ea5-4ad1-a975-cda0a8af2b28@amd.com>
Date: Tue, 11 Feb 2025 14:38:47 -0600
From: "Bowman, Terry" <terry.bowman@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: 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
Subject: Re: [PATCH v7 03/17] CXL/PCI: Introduce PCIe helper functions
 pcie_is_cxl() and pcie_is_cxl_port()



On 2/11/2025 2:28 PM, Bjorn Helgaas wrote:
> On Tue, Feb 11, 2025 at 01:24:30PM -0600, 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>
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
>
> But I would change the subject to:
>
>   PCI/CXL: ...
>
> since this only changes drivers/pci files.

I'll change to PCI/CXL. Thanks for the review and 'acks'.

Terry
>> ---
>>  drivers/pci/pci.c             | 13 +++++++++++++
>>  drivers/pci/probe.c           | 10 ++++++++++
>>  include/linux/pci.h           |  5 +++++
>>  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 869d204a70a3..a2d8b41dd043 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -5032,6 +5032,19 @@ static u16 cxl_port_dvsec(struct pci_dev *dev)
>>  					 PCI_DVSEC_CXL_PORT);
>>  }
>>  
>> +inline bool pcie_is_cxl(struct pci_dev *pci_dev)
>> +{
>> +	return pci_dev->is_cxl;
>> +}
>> +
>> +bool pcie_is_cxl_port(struct pci_dev *dev)
>> +{
>> +	if (!pcie_is_cxl(dev))
>> +		return false;
>> +
>> +	return (cxl_port_dvsec(dev) > 0);
>> +}
>> +
>>  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 b6536ed599c3..7737b9ce7a83 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -1676,6 +1676,14 @@ 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);
>> @@ -2006,6 +2014,8 @@ 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);
>>  
>>  	if (pci_is_pcie(dev))
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 1d62e785ae1f..82a0401c58d3 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
>> @@ -741,6 +742,10 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
>>  	return false;
>>  }
>>  
>> +bool pcie_is_cxl(struct pci_dev *pci_dev);
>> +
>> +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 3445c4970e4d..dbc0f23d8c82 100644
>> --- a/include/uapi/linux/pci_regs.h
>> +++ b/include/uapi/linux/pci_regs.h
>> @@ -1208,9 +1208,10 @@
>>  #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 */
>> -- 
>> 2.34.1
>>