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: <a2fc0134-5b6d-4778-aef2-4447c50eb430@amd.com>
Date: Tue, 14 Jan 2025 09:19:12 -0600
From: "Bowman, Terry" <terry.bowman@....com>
To: Ira Weiny <ira.weiny@...el.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,
 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()




On 1/13/2025 5:49 PM, Ira Weiny wrote:
> 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.

Hi Ira,

Thanks for reviewing. Is this what you are looking for here:

+bool pcie_is_cxl_port(struct pci_dev *dev)
+{
+	return (cxl_port_dvsec(dev) > 0);

>> +}
>> +
> [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
Ok,

Thanks for reviewing the patches.

Regards,
Terry
> [snip]