[RFC PATCH v4 33/38] Documentation: PCI: endpoint: pci-epf-vntb: Update and add mwN_offset usage
From: Koichiro Den <hidden>
Date: 2026-01-18 13:55:55
Also in:
dmaengine, linux-devicetree, linux-doc, linux-iommu, linux-kselftest, linux-pci, linux-renesas-soc, lkml
Subsystem:
documentation, pci endpoint subsystem, pci subsystem, the rest · Maintainers:
Jonathan Corbet, Manivannan Sadhasivam, Krzysztof Wilczyński, Bjorn Helgaas, Linus Torvalds
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 <redacted> --- 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 --------------------------------------------
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2.51.0