linux-kernel - Re: [PATCH v13 01/25] CXL/PCI: Move CXL DVSEC definitions into uapi/linux/pci

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Message-ID: <69337bc4d1943_1b2e100a9@dwillia2-mobl4.notmuch>
Date: Fri, 5 Dec 2025 16:41:40 -0800
From: <dan.j.williams@...el.com>
To: Bjorn Helgaas <helgaas@...nel.org>, Terry Bowman <terry.bowman@....com>
CC: <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>,
	<linux-cxl@...r.kernel.org>, <alucerop@....com>, <ira.weiny@...el.com>,
	<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v13 01/25] CXL/PCI: Move CXL DVSEC definitions into
 uapi/linux/pci_regs.h

Bjorn Helgaas wrote:
> On Mon, Nov 03, 2025 at 06:09:37PM -0600, Terry Bowman wrote:
> > The CXL DVSECs are currently defined in cxl/core/cxlpci.h. These are not
> > accessible to other subsystems. Move these to uapi/linux/pci_regs.h.
> > 
> > Change DVSEC name formatting to follow the existing PCI format in
> > pci_regs.h. The current format uses CXL_DVSEC_XYZ and the CXL defines must
> > be changed to be PCI_DVSEC_CXL_XYZ to match existing pci_regs.h. Leave
> > PCI_DVSEC_CXL_PORT* defines as-is because they are already defined and may
> > be in use by userspace application(s).
> > 
> > Update existing usage to match the name change.
> > 
> > Update the inline documentation to refer to latest CXL spec version.
> 
> > +++ b/drivers/pci/pci.c
> > @@ -5002,7 +5002,9 @@ static bool cxl_sbr_masked(struct pci_dev *dev)
> >  	if (!dvsec)
> >  		return false;
> >  
> > -	rc = pci_read_config_word(dev, dvsec + PCI_DVSEC_CXL_PORT_CTL, &reg);
> > +	rc = pci_read_config_word(dev,
> > +				  dvsec + PCI_DVSEC_CXL_PORT_CTL,
> > +				  &reg);
> 
> Stray change.
> 
> > +++ b/include/uapi/linux/pci_regs.h
> > @@ -1244,9 +1244,64 @@
> >  /* 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) */
> > -#define PCI_DVSEC_CXL_PORT				3
> > -#define PCI_DVSEC_CXL_PORT_CTL				0x0c
> > -#define PCI_DVSEC_CXL_PORT_CTL_UNMASK_SBR		0x00000001
> > +/* 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_HEADER1_LENGTH_MASK  __GENMASK(31, 20)
> 
> Looks like a functional duplicate of PCI_DVSEC_HEADER1_LEN().
> 
> Why __GENMASK() instead of GENMASK()?  I don't know the purpose of
> __GENMASK(), but I see other include/uapi/ files using GENMASK().
> Maybe they're wrong?
> 
> Same questions for _BITUL() below.

See this commit:

3c7a8e190bc5 uapi: introduce uapi-friendly macros for GENMASK

GENMASK() for a long time was not available to uapi headers since uapi
headers can only include other include/uapi/ headers, not
include/linux/. That commit made some common kernel bitfield helpers
finally available to the uapi side of the house.