fix(linux): Enhance PCIe Backplane documentation for multiple SoCs

Improve the PCIe backplane documentation to accommodate information for
all the supported SoCs (J721E, J784S4, J742S2). Update the DTB overlay
file used to test the backplane functionality.

Signed-off-by: Aksh Garg <a-garg7@ti.com>

Author: AkshGarg-19

source/linux/Foundational_Components/Kernel/Kernel_Drivers/PCIe/PCIe_Backplane.rst

@@ -14,11 +14,11 @@ endpoint controller. Each host should be connected to a separate endpoint
 controller instance and each host will enumerate the other host as an
 independent function.
 
-PCIe uses NTB (non transparent bridge) for two hosts to communicate with each
-other. Though J721E doesn't have an explicit NTB controller, NTB functionality
-can be achieved using multiple endpoint controller instances. And for PCIe
-backplane (to connect more than 2 hosts), aggregation of NTB controllers
-can be modeled using multiple instances of multi-function endpoint controller.
+PCIe uses NTB (Non Transparent Bridge) for two hosts to communicate with each
+other. Though |__PART_FAMILY_DEVICE_NAMES__| does not have an explicit NTB
+controller, multiple endpoint controller instances provide NTB functionality.
+For PCIe backplane (to connect more than 2 hosts), multiple instances of
+multi-function endpoint controller create the aggregation of NTB controllers.
 
 In the below diagram, PCI NTB function configures the SoC with multiple
 PCIe Endpoint (EP) instances in such a way that transaction from one EP
@@ -63,6 +63,12 @@ the endpoint side NTB architecture.
 The following picture shows J721E EVM connected to two DRA7 EVMs. Here the two
 DRA7x boards communicate with each other using J721E as backplane.
 
+.. ifconfig:: CONFIG_part_variant in ('J784S4','J742S2')
+
+  Similarly, |__PART_FAMILY_DEVICE_NAMES__| can be connected to two hosts, who
+  can communicate with each other using |__PART_FAMILY_DEVICE_NAMES__|
+  as backplane.
+
 .. Image:: /images/j721e-backplane.jpg
 
 
@@ -71,21 +77,34 @@ DRA7x boards communicate with each other using J721E as backplane.
 
 .. rubric:: *Backplane DTS Overlay File*
 
-The following DTS overlay file configures the PCIe controller in EP mode and
-also contains a device tree node to create a NTB function device:
+The following DTS overlay files configure both the PCIe controller in EP mode
+required for NTB functionality:
 
-::
+.. ifconfig:: CONFIG_part_variant in ('J784S4','J742S2')
 
-  arch/arm64/boot/dts/ti/k3-j721e-pcie-backplane.dtso
+   * :file:`arch/arm64/boot/dts/ti/k3-j784s4-evm-pcie0-pcie1-ep.dtso`
 
-In order to apply the dts overlay file, the following command should be given
+.. ifconfig:: CONFIG_part_variant not in ('J784S4','J742S2')
+
+   * :file:`arch/arm64/boot/dts/ti/k3-j721e-evm-pcie0-ep.dtso`
+   * :file:`arch/arm64/boot/dts/ti/k3-j721e-evm-pcie1-ep.dtso`
+
+In order to apply the dts overlay files, the following command should be given
 in u-boot prompt:
 
-::
+.. ifconfig:: CONFIG_part_variant in ('J784S4','J742S2')
 
-  #setenv name_overlays ti/k3-j721e-pcie-backplane.dtbo
+   .. code-block:: console
 
-.. rubric:: *EP Side Configuration (J721E Backplane)*
+      setenv name_overlays ti/k3-j784s4-evm-pcie0-pcie1-ep.dtbo
+
+.. ifconfig:: CONFIG_part_variant not in ('J784S4','J742S2')
+
+   .. code-block:: console
+
+      setenv name_overlays ti/k3-j721e-evm-pcie0-ep.dtbo ti/k3-j721e-evm-pcie1-ep.dtbo
+
+.. rubric:: *EP Side Configuration (Backplane)*
    :name: ep-side-configuration
 
 .. rubric:: **Dip switch settings**
@@ -100,9 +119,9 @@ in u-boot prompt:
   Both PCIe instances should be configured in EP mode by setting
   PCIE_1L_MODE_SEL (switch 5) and PCIE_2L_MODE_SEL (switch 6) in sw3 to '1'.
 
-.. rubric:: **8.x SDK (5.10 Kernel)**
+.. rubric:: **EP Backplane Configuration Steps**
 
-The following set of steps is required only for 5.10 Kernel
+The following steps are required to configure the PCIe endpoints as a backplane:
 
     .. rubric:: Creating pci-epf-ntb device
 
@@ -111,6 +130,7 @@ The following set of steps is required only for 5.10 Kernel
 
     ::
 
+        # modprobe pci_epf_ntb
         # mount -t configfs none /sys/kernel/config
         # cd /sys/kernel/config/pci_ep/
         # mkdir functions/pci_epf_ntb/func1
@@ -151,15 +171,8 @@ The following set of steps is required only for 5.10 Kernel
         # echo 0x104c > functions/pci_epf_ntb/func1/vendorid
         # echo 0xb00d > functions/pci_epf_ntb/func1/deviceid
 
-    In order to configure NTB specific attributes, a new sub-directory to func1
-    should be created
-
-    ::
-
-        # mkdir functions/pci_epf_ntb/func1/pci_epf_ntb.0/
-
-    The NTB function driver will populate this directory with various attributes
-    that can be configured by the user
+    The NTB function driver also populates func1/pci_epf_ntb.0 directory with
+    various attributes that can be configured by the user
 
     ::
 
@@ -188,13 +201,13 @@ The following set of steps is required only for 5.10 Kernel
 
     ::
 
-        # ln -s controllers/2900000.pcie-ep/ functions/pci-epf-ntb/func1/primary
-        # ln -s controllers/2910000.pcie-ep/ functions/pci-epf-ntb/func1/secondary
+        # ln -s controllers/2900000.pcie-ep/ functions/pci_epf_ntb/func1/primary
+        # ln -s controllers/2910000.pcie-ep/ functions/pci_epf_ntb/func1/secondary
 
     Once the above step is completed, both the PCI endpoint controllers are ready to
     establish a link with the host.
 
-    .. rubric:: Start the Link: 7.x and 8.x SDK (5.4 and 5.10 Kernel)
+    .. rubric:: Start the Link:
 
     In order for the endpoint device to establish a link with the host, the _start_
     field should be populated with '1'. For NTB, both the PCI endpoint controllers
@@ -205,9 +218,6 @@ The following set of steps is required only for 5.10 Kernel
         # echo 1 > controllers/2900000.pcie-ep/start
         # echo 1 > controllers/2910000.pcie-ep/start
 
-(PCIe2 can also be configured for NTB, but that is not
-tested yet).
-
 .. rubric:: *RC Side Configuration*
    :name: rc-side-configuration
 
@@ -221,6 +231,7 @@ existing driver.
 
 ::
 
+  modprobe ntb_hw_epf
   echo 0000:01:00.0 > /sys/bus/pci/devices/0000\:01\:00.0/driver/unbind
 
 After unbinding from existing driver, it should be bound to ntb_hw_epf driver.
@@ -241,14 +252,14 @@ hosts.
 .. rubric:: **Kernel Configs**
    :name: kernel-configs
 
-.. rubric:: *EP Side (J721E Backplane)*
+.. rubric:: *EP Side (Backplane)*
    :name: ep-side-configs
 
 ::
 
   CONFIG_PCI_ENDPOINT=y
   CONFIG_PCI_ENDPOINT_CONFIGFS=y
-  CONFIG_PCI_EPF_NTB=y
+  CONFIG_PCI_EPF_NTB=m
   CONFIG_PCI_J721E=y
   CONFIG_PCIE_CADENCE=y
   CONFIG_PCIE_CADENCE_EP=y
@@ -274,5 +285,5 @@ For additional information, please refer to:
 
 ::
 
-  <Processor_SDK_install_dir>/board-support/linux-[ver]/Documentation/PCI/endpoint/pci-test-ntb.txt
+  <Processor_SDK_install_dir>/board-support/linux-[ver]/Documentation/PCI/endpoint/pci-ntb-function.rst