linux-kernel - Re: [RESEND v13 02/25] PCI/CXL: Introduce pcie_is

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Message-ID: <20251104175223.00004e02@huawei.com>
Date: Tue, 4 Nov 2025 17:52:23 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Terry Bowman <terry.bowman@....com>
CC: <dave@...olabs.net>, <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>,
	<linux-cxl@...r.kernel.org>, <alucerop@....com>, <ira.weiny@...el.com>,
	<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [RESEND v13 02/25] PCI/CXL: Introduce pcie_is_cxl()

On Tue, 4 Nov 2025 11:02:42 -0600
Terry Bowman <terry.bowman@....com> wrote:

> CXL and AER drivers need the ability to identify CXL devices.
> 
> Introduce set_pcie_cxl() with logic checking for CXL.mem or CXL.cache
> status in the CXL Flexbus DVSEC status register. 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
> CXL.cache and CXl.mem status.
> 
> In the case the device is an EP or USP, call set_pcie_cxl() on behalf of
> the parent downstream device. Once a device is created there is
> possibilty the parent training or CXL state was updated as well. This
> will make certain the correct parent CXL state is cached.
> 
> 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>
> Reviewed-by: Alejandro Lucero <alucerop@....com>
> Reviewed-by: Ben Cheatham <benjamin.cheatham@....com>
> 
Hi Terry,

Drag the FLEXBUS_STATUS defines from previous patch to this one and we
are all good I think. At least it wasn't far :)

Jonathan

> ---
> 
> Changes in v12->v13:
> - Add Ben's "reviewed-by"
> 
> Changes in v11->v12:
> - Add review-by for Alejandro
> - Add comment in set_pcie_cxl() explaining why updating parent status.
> 
> Changes in v10->v11:
> - Amend set_pcie_cxl() to check for Upstream Port's and EP's parent
>   downstream port by calling set_pcie_cxl(). (Dan)
> - Retitle patch: 'Add' -> 'Introduce'
> - Add check for CXL.mem and CXL.cache (Alejandro, Dan)
> ---
>  drivers/pci/probe.c | 29 +++++++++++++++++++++++++++++
>  include/linux/pci.h |  6 ++++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 0ce98e18b5a8..63124651f865 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1709,6 +1709,33 @@ static void set_pcie_thunderbolt(struct pci_dev *dev)
>  		dev->is_thunderbolt = 1;
>  }
>  
> +static void set_pcie_cxl(struct pci_dev *dev)
> +{
> +	struct pci_dev *parent;
> +	u16 dvsec = pci_find_dvsec_capability(dev, PCI_VENDOR_ID_CXL,
> +					      PCI_DVSEC_CXL_FLEXBUS_PORT);
> +	if (dvsec) {
> +		u16 cap;
> +
> +		pci_read_config_word(dev, dvsec + PCI_DVSEC_CXL_FLEXBUS_STATUS_OFFSET, &cap);
> +
> +		dev->is_cxl = FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_STATUS_CACHE_MASK, cap) ||
> +			FIELD_GET(PCI_DVSEC_CXL_FLEXBUS_STATUS_MEM_MASK, cap);
> +	}
> +
> +	if (!pci_is_pcie(dev) ||
> +	    !(pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT ||
> +	      pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM))
> +		return;
> +
> +	/*
> +	 * Update parent's CXL state because alternate protocol training
> +	 * may have changed
> +	 */
> +	parent = pci_upstream_bridge(dev);
> +	set_pcie_cxl(parent);
> +}