Re: [RFC PATCH 1/3] PCI: Add PCIe Gen 7 (128 GT/s) register and speed definitions

[Ilpo Järvinen]

On Tue, 17 Feb 2026, Ionut Nechita (Sunlight Linux) wrote:

> From: Ionut Nechita <ionut_n2001@xxxxxxxxx>
> 
> Add register definitions for PCIe Gen 7 128 GT/s link speed:
> 
>   - PCI_EXP_LNKCAP_SLS_128_0GB (encoding 0x7)
>   - PCI_EXP_LNKCAP2_SLS_128_0GB (bit 6 in Supported Link Speeds Vector)
>   - PCI_EXP_LNKCTL2_TLS_128_0GT (Target Link Speed 0x7)
>   - PCIE_SPEED_128_0GT enum value (0x1a)
> 
> Widen pci_dev.supported_speeds from u8 to u16 to accommodate the
> expanded Supported Link Speeds Vector which now uses bits 1-7.
> 
> PCIe Gen 7 doubles the data rate to 128 GT/s using PAM4 signaling
> with mandatory Flit mode encoding (1:1, no overhead), providing
> up to 256 GB/s unidirectional (512 GB/s bi-directional) bandwidth
> on an x16 link.
> 
> Note: Based on the PCIe 7.0 specification announced by PCI-SIG in
> 2022, targeted for member release in 2025. No hardware exists yet

2022?

Please provide more precise spec reference(s) with section numbers (as per 
the usual custom).

> to validate these definitions.
> 
> Signed-off-by: Ionut Nechita <ionut_n2001@xxxxxxxxx>
> ---
>  include/linux/pci.h           | 3 ++-
>  include/uapi/linux/pci_regs.h | 3 +++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index b5cc0c2b99065..21dd6ea5beb6d 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -303,6 +303,7 @@ enum pci_bus_speed {
>  	PCIE_SPEED_16_0GT		= 0x17,
>  	PCIE_SPEED_32_0GT		= 0x18,
>  	PCIE_SPEED_64_0GT		= 0x19,
> +	PCIE_SPEED_128_0GT		= 0x1a,
>  	PCI_SPEED_UNKNOWN		= 0xff,
>  };
>  
> @@ -558,7 +559,7 @@ struct pci_dev {
>  	struct pci_tsm *tsm;		/* TSM operation state */
>  #endif
>  	u16		acs_cap;	/* ACS Capability offset */
> -	u8		supported_speeds; /* Supported Link Speeds Vector */
> +	u16		supported_speeds; /* Supported Link Speeds Vector */
>  	phys_addr_t	rom;		/* Physical address if not from BAR */
>  	size_t		romlen;		/* Length if not from BAR */
>  	/*
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index 3add74ae25948..fa00c6ca9f382 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -545,6 +545,7 @@
>  #define  PCI_EXP_LNKCAP_SLS_16_0GB 0x00000004 /* LNKCAP2 SLS Vector bit 3 */
>  #define  PCI_EXP_LNKCAP_SLS_32_0GB 0x00000005 /* LNKCAP2 SLS Vector bit 4 */
>  #define  PCI_EXP_LNKCAP_SLS_64_0GB 0x00000006 /* LNKCAP2 SLS Vector bit 5 */
> +#define  PCI_EXP_LNKCAP_SLS_128_0GB 0x00000007 /* LNKCAP2 SLS Vector bit 6 */

Eh, did you make this up? This is not at all what is in the PCIe 7.0 spec!

>  #define  PCI_EXP_LNKCAP_MLW	0x000003f0 /* Maximum Link Width */
>  #define  PCI_EXP_LNKCAP_ASPMS	0x00000c00 /* ASPM Support */
>  #define  PCI_EXP_LNKCAP_ASPM_L0S 0x00000400 /* ASPM L0s Support */
> @@ -693,6 +694,7 @@
>  #define  PCI_EXP_LNKCAP2_SLS_16_0GB	0x00000010 /* Supported Speed 16GT/s */
>  #define  PCI_EXP_LNKCAP2_SLS_32_0GB	0x00000020 /* Supported Speed 32GT/s */
>  #define  PCI_EXP_LNKCAP2_SLS_64_0GB	0x00000040 /* Supported Speed 64GT/s */
> +#define  PCI_EXP_LNKCAP2_SLS_128_0GB	0x00000080 /* Supported Speed 128GT/s */

This is simplifying this too much, the spec says "128 GT/s or higher".

The actual speeds are in the new 128 GT/s Capability and should be 
read from there.

>  #define  PCI_EXP_LNKCAP2_CROSSLINK	0x00000100 /* Crosslink supported */
>  #define PCI_EXP_LNKCTL2		0x30	/* Link Control 2 */
>  #define  PCI_EXP_LNKCTL2_TLS		0x000f
> @@ -702,6 +704,7 @@
>  #define  PCI_EXP_LNKCTL2_TLS_16_0GT	0x0004 /* Supported Speed 16GT/s */
>  #define  PCI_EXP_LNKCTL2_TLS_32_0GT	0x0005 /* Supported Speed 32GT/s */
>  #define  PCI_EXP_LNKCTL2_TLS_64_0GT	0x0006 /* Supported Speed 64GT/s */
> +#define  PCI_EXP_LNKCTL2_TLS_128_0GT	0x0007 /* Supported Speed 128GT/s */

This is wrong as well.

This entire change (the whole series) is not going to be as 
straightforward as you assumed.

>  #define  PCI_EXP_LNKCTL2_ENTER_COMP	0x0010 /* Enter Compliance */
>  #define  PCI_EXP_LNKCTL2_TX_MARGIN	0x0380 /* Transmit Margin */
>  #define  PCI_EXP_LNKCTL2_HASD		0x0020 /* HW Autonomous Speed Disable */

-- 
 i.