On Thu, Jan 08, 2026 at 07:29:27PM +0100, Janusz Krzysztofik wrote:
> Hi,
>
> Before I submit patches, I'd like you to have a look at the below provided
> example of proposed output from a modified lsgpu tool and share your comments.
>
> Users complain about PCIe link bandwith of their Intel discrete GPU devices
> limited to 2.5 GT/s x1, unable to utilize capabilities of their motherboards,
> see https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/10753. So far
> Intel has provided the following explanation:
> https://www.intel.com/content/www/us/en/support/articles/000094587/graphics.html
>
> That's not true. While PCI devices associated directly with Intel discrete
> GPUs provide fake data about link speed and width capabilities and status,
> their upstream PCIe bridges report correct, actual values of those link
> bandwidth attributes.
Last time I was looking at this, and I have some doubts:
Examining PCIe link chain for BMG, in my case device is
0000:03:00.0 ->
../../../devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0
LnkCap looks like this:
# lspci -vv -s 0000:00:01.0 | egrep '^[0-9]|LnkCap'
00:01.0 PCI bridge: Intel Corporation Device a70d (rev 01) (prog-if 00 [Normal
decode])
LnkCap: Port #2, Speed 32GT/s, Width x16, ASPM L1, Exit Latency
L1 <16us
LnkCap2: Supported Link Speeds: 2.5-32GT/s, Crosslink- Retimer+
2Retimers+ DRS-
# lspci -vv -s 0000:01:00.0 | egrep '^[0-9]|LnkCap'
01:00.0 PCI bridge: Intel Corporation Device e2ff (rev 01) (prog-if 00 [Normal
decode])
LnkCap: Port #0, Speed 16GT/s, Width x8, ASPM L1, Exit Latency
L1 <32us
LnkCap2: Supported Link Speeds: 2.5-16GT/s, Crosslink- Retimer+
2Retimers+ DRS+
# lspci -vv -s 0000:02:01.0 | egrep '^[0-9]|LnkCap'
02:01.0 PCI bridge: Intel Corporation Device e2f0 (prog-if 00 [Normal decode])
LnkCap: Port #8, Speed 2.5GT/s, Width x1, ASPM L1, Exit Latency
L1 <1us
LnkCap2: Supported Link Speeds: 2.5GT/s, Crosslink- Retimer+
2Retimers+ DRS-
# lspci -vv -s 0000:03:00.0 | egrep '^[0-9]|LnkCap'
03:00.0 VGA compatible controller: Intel Corporation Device e20b (prog-if 00
[VGA controller])
LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s L1, Exit
Latency L0s <64ns, L1 <1us
LnkCap2: Supported Link Speeds: 2.5GT/s, Crosslink- Retimer-
2Retimers- DRS-
What is real link speed/width here? 32GT/s? 16GT/s? 2.5GT/s? Even if we
put 16GT/s here or even 32GT/s (why not, it is in the chain) we still
really don't know what is the real link speed/width on the GPU side.
We will provide then two different values - lspci will show one value,
lsgpu another. I don't know is it possible to alter sysfs values to real
link speed/width (assuming it is a lie now) but imo real fix should go
to sysfs side, not to userspace apps which just read what kernel provides.
--
Zbigniew
>
> While users may use lspci tool to examine bridge devices manually themselves,
> there is an idea of extending our lsgpu tool with support for printing that
> data. In order for the tool to show correct link bandwidth of a discrete
> GPU,
> we need to identify its PCIe upstream bridge and get that information from
> that bridge. For consistency with lspci output, we are not going to replace
> silently the fake data with those obtained from the bridge, only omit that
> data from our list of the GPU PCI device attributes, and complement the
> printout with more or less complete information about the bridge itself.
>
> Please have a look at the example output provided below and share your
> comments, if any.
>
> $ sudo ./build/tools/lsgpu -s
> sys:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0/drm/card0
> subsystem : drm
> drm card : /dev/dri/card0
> parent :
> sys:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0
>
> sys:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0/drm/renderD128
> subsystem : drm
> drm render : /dev/dri/renderD128
> parent :
> sys:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0
>
> sys:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0
> subsystem : pci
> drm card : /dev/dri/card0
> drm render : /dev/dri/renderD128
> vendor : 8086
> device : 56A0
> codename : dg2
> bridge : sys:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0
>
> sys:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0
> subsystem : pci
> vendor : 8086
> device : 4FA0
>
> $ sudo ./build/tools/lsgpu -p
> ==========
> drm:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0/drm/card0
> ==========
>
> [properties]
> DEVPATH :
> /devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0/drm/card0
> ID_PATH_TAG : pci-0000_03_00_0
> CURRENT_TAGS : :seat:uaccess:master-of-seat:
> TAGS : :seat:uaccess:master-of-seat:
> MINOR : 0
> DEVNAME : /dev/dri/card0
> ID_PATH : pci-0000:03:00.0
> SUBSYSTEM : drm
> DEVTYPE : drm_minor
> DEVLINKS : /dev/dri/by-path/pci-0000:03:00.0-card
> ID_FOR_SEAT : drm-pci-0000_03_00_0
> USEC_INITIALIZED : 7056426
> MAJOR : 226
>
> [attributes]
> gt_cur_freq_mhz : 600
> gt_act_freq_mhz : 0
> subsystem : drm
> gt_max_freq_mhz : 2400
> gt_RP1_freq_mhz : 600
> gt_RPn_freq_mhz : 300
> device : 0000:03:00.0
> gt_boost_freq_mhz : 2400
> gt_RP0_freq_mhz : 2400
> error : No error state collected
> gt_min_freq_mhz : 300
> dev : 226:0
>
> ==========
> drm:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0/drm/renderD128
> ==========
>
> [properties]
> DEVPATH :
> /devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0/drm/renderD128
> ID_PATH : pci-0000:03:00.0
> MINOR : 128
> DEVNAME : /dev/dri/renderD128
> ID_PATH_TAG : pci-0000_03_00_0
> SUBSYSTEM : drm
> DEVTYPE : drm_minor
> DEVLINKS : /dev/dri/by-path/pci-0000:03:00.0-render
> USEC_INITIALIZED : 7057304
> MAJOR : 226
>
> [attributes]
> subsystem : drm
> dev : 226:128
> device : 0000:03:00.0
>
> ==========
> pci:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0
> ==========
> card device : /dev/dri/card0
> render device : /dev/dri/renderD128
> codename : dg2
>
> [properties]
> PCI_ID : 8086:56A0
> DEVPATH :
> /devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:01.0/0000:03:00.0
> ID_PCI_INTERFACE_FROM_DATABASE : VGA controller
> ID_PATH_TAG : pci-0000_03_00_0
> PCI_CLASS : 30000
> ID_PCI_CLASS_FROM_DATABASE : Display controller
> ID_PCI_SUBCLASS_FROM_DATABASE : VGA compatible controller
> PCI_SUBSYS_ID : 8086:1029
> MODALIAS :
> pci:v00008086d000056A0sv00008086sd00001029bc03sc00i00
> PCI_SLOT_NAME : 0000:03:00.0
> USEC_INITIALIZED : 7056140
> DRIVER : i915
> ID_PATH : pci-0000:03:00.0
> SUBSYSTEM : pci
>
> [attributes]
> consistent_dma_mask_bits : 46
> power_state : D0
> class : 0x030000
> subsystem : pci
> iommu_group : 17
> enable : 1
> subsystem_vendor : 0x8086
> reset_method : flr bus
> vendor : 0x8086
> boot_vga : 1
> resource2_resize : 0000000000007f00
> subsystem_device : 0x1029
> driver : i915
> iommu : dmar0
> d3cold_allowed : 1
> local_cpulist : 0-23
> ari_enabled : 1
> numa_node : -1
> dma_mask_bits : 46
> irq : 124
> driver_override : (null)
> device : 0x56a0
> local_cpus : ffffff
> revision : 0x08
> msi_bus : 1
> broken_parity_status : 0
> devspec :
>
> ========== pci:/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0 ==========
>
> [properties]
> PCI_ID : 8086:4FA0
> DEVPATH :
> /devices/pci0000:00/0000:00:01.0/0000:01:00.0
> ID_PCI_INTERFACE_FROM_DATABASE : Normal decode
> ID_PATH_TAG : pci-0000_01_00_0
> PCI_CLASS : 60400
> ID_PCI_CLASS_FROM_DATABASE : Bridge
> ID_PCI_SUBCLASS_FROM_DATABASE : PCI bridge
> PCI_SUBSYS_ID : 0000:0000
> MODALIAS :
> pci:v00008086d00004FA0sv00000000sd00000000bc06sc04i00
> PCI_SLOT_NAME : 0000:01:00.0
> USEC_INITIALIZED : 7055925
> DRIVER : pcieport
> ID_PATH : pci-0000:01:00.0
> SUBSYSTEM : pci
>
> [attributes]
> firmware_node : device:04
> irq : 16
> iommu_group : 14
> reset_method : bus
> device : 0x4fa0
> d3cold_allowed : 1
> broken_parity_status : 0
> consistent_dma_mask_bits : 32
> numa_node : -1
> local_cpus : ffffff
> subsystem : pci
> iommu : dmar0
> enable : 1
> subsystem_vendor : 0x0000
> secondary_bus_number : 2
> current_link_speed : 16.0 GT/s PCIe
> max_link_width : 16
> vendor : 0x8086
> max_link_speed : 16.0 GT/s PCIe
> msi_bus : 1
> current_link_width : 16
> dma_mask_bits : 32
> driver_override : (null)
> ari_enabled : 0
> class : 0x060400
> local_cpulist : 0-23
> revision : 0x01
> subordinate_bus_number : 4
> subsystem_device : 0x0000
> driver : pcieport
> devspec :
> power_state : D0
>
>
> A few AER related attributes that provide error statistics in the form of
> hard to format lists of multiple key-values pairs each have been omitted form
> the printout.
>
> Thanks,
> Janusz
>
>
