[RFC PATCH v4 33/38] Documentation: PCI: endpoint: pci-epf-vntb: Update and add mwN_offset usage

Koichiro Den
2026-01-18T13:55:55Z

Add a concrete example showing how to pack multiple memory windows into
a single BAR by using 'mwN_bar' and 'mwN_offset'.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
Documentation/PCI/endpoint/pci-vntb-howto.rst | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/Documentation/PCI/endpoint/pci-vntb-howto.rst b/Documentation/PCI/endpoint/pci-vntb-howto.rst
index 3679f5c30254..097826f946a9 100644
--- a/Documentation/PCI/endpoint/pci-vntb-howto.rst
+++ b/Documentation/PCI/endpoint/pci-vntb-howto.rst
@@ -90,9 +90,9 @@ of the function device and is populated with the following NTB specific
attributes that can be configured by the user::

# ls functions/pci_epf_vntb/func1/pci_epf_vntb.0/
- ctrl_bar db_count mw1_bar mw2_bar mw3_bar mw4_bar spad_count
- db_bar mw1 mw2 mw3 mw4 num_mws vbus_number
- vntb_vid vntb_pid
+ ctrl_bar mw1 mw2 mw3 mw4 num_mws vntb_pid
+ db_bar mw1_bar mw2_bar mw3_bar mw4_bar spad_count vntb_vid
+ db_count mw1_offset mw2_offset mw3_offset mw4_offset vbus_number

A sample configuration for NTB function is given below::

@@ -111,6 +111,19 @@ A sample configuration for virtual NTB driver for virtual PCI bus::
# echo 0x080A > functions/pci_epf_vntb/func1/pci_epf_vntb.0/vntb_pid
# echo 0x10 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/vbus_number

+When BAR resources are tight but you still need to create many memory
+windows, you can pack multiple windows into a single BAR by setting
+``mwN_bar`` to the same BAR number and using ``mwN_offset`` to place each
+MW within that BAR. Offsets are in bytes and the resulting regions must not
+overlap and must exactly fit within the BAR size. This may fail depending
+on the underlying EPC capabilities::
+
+ # echo 0xE0000 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/mw1
+ # echo 0x20000 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/mw2
+ # echo 0xE0000 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/mw2_offset
+ # echo 2 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/mw1_bar
+ # echo 2 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/mw2_bar
+
Binding pci-epf-vntb Device to EP Controller
--------------------------------------------

--
2.51.0