linux-kernel - [RFC PATCH 25/25] Documentation: PCI: endpoint: pci-epf-vntb: Update and add mwN

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Message-ID: <20251023071916.901355-26-den@valinux.co.jp>
Date: Thu, 23 Oct 2025 16:19:16 +0900
From: Koichiro Den <den@...inux.co.jp>
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Subject: [RFC PATCH 25/25] Documentation: PCI: endpoint: pci-epf-vntb: Update and add mwN_offset usage

Add a concrete example showing how to place two memory windows in the
same BAR (one for data, one for interrupts) by using 'mwN_offset' and
'mwN_bar'. This is useful when BAR resources are scarce and is aligned
with recent endpoint-side inbound mapping support.

Note that part of the `ls` delta covers missing doc update for
attributes that were introduced in the commit e7cd58d2fdf8 ("PCI:
endpoint: pci-epf-vntb: Allow BAR assignment via configfs")

Signed-off-by: Koichiro Den <den@...inux.co.jp>
---
 Documentation/PCI/endpoint/pci-vntb-howto.rst | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/Documentation/PCI/endpoint/pci-vntb-howto.rst b/Documentation/PCI/endpoint/pci-vntb-howto.rst
index 70d3bc90893f..142cf9244cc6 100644
--- a/Documentation/PCI/endpoint/pci-vntb-howto.rst
+++ b/Documentation/PCI/endpoint/pci-vntb-howto.rst
@@ -90,8 +90,10 @@ 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/
-	db_count    mw1         mw2         mw3         mw4         num_mws
-	spad_count
+	ctrl_bar  mw1_bar     mw2_offset  mw4         spad_count
+	db_bar    mw1_offset  mw3         mw4_bar     vbus_number
+	db_count  mw2         mw3_bar     mw4_offset  vntb_pid
+	mw1       mw2_bar     mw3_offset  num_mws     vntb_vid
 
 A sample configuration for NTB function is given below::
 
@@ -106,6 +108,16 @@ 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 want to enable interrupts (which
+require a dedicated MW in addition to the data MW), map both MWs into a
+single BAR via 'mwN_offset' and 'mwN_bar' as shown below::
+
+	# echo 0xF0000 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/mw1
+	# echo 0x8000 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/mw2
+	# echo 0xF0000 > 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-ntb Device to EP Controller
 --------------------------------------------
 
-- 
2.48.1