fix(linux): Add PCIe resource reallocation note for VF enumeration

Add a note to the PCIe Root Complex documentation about using 'pci=realloc'
bootargs parameter when the root complex is connected to an endpoint with
Virtual Functions and kernel panics during enumeration. This parameter
instructs the Linux kernel to reallocate PCI bridge resources, helping
to resolve conflicts during PCIe device enumeration.

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

Author: AkshGarg-19

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

@@ -146,70 +146,84 @@ Following is a brief explanation of layers shown in the diagram:
 
 .. ifconfig:: CONFIG_part_family in ('AM64X_family','J7_family')
 
-    .. rubric:: **RC Device Configuration**
-       :name: rc-device-configuration
+   .. rubric:: **RC Device Configuration**
+      :name: rc-device-configuration
 
-    .. rubric:: *DTS Modification*
-       :name: rc-dts-modification
+   .. rubric:: *DTS Modification*
+      :name: rc-dts-modification
 
-    The default dts for |__PART_FAMILY_DEVICE_NAMES__| is configured to be used in
-    root complex mode.
+   The default dts for |__PART_FAMILY_DEVICE_NAMES__| is configured to be used in
+   root complex mode.
 
-    .. rubric:: *Linux Driver Configuration*
-       :name: linux-driver-configuration
+   .. rubric:: *Linux Driver Configuration*
+      :name: linux-driver-configuration
 
-    The following config options have to be enabled in order to configure the
-    PCI controller to be used in Root Complex mode.
+   The following config options have to be enabled in order to configure the
+   PCI controller to be used in Root Complex mode.
 
-    ::
+   ::
+
+      CONFIG_SOCIONEXT_SYNQUACER_PREITS=y
+      CONFIG_PCI=y
+      CONFIG_PCI_MSI=y
+      CONFIG_PCI_J721E=y
+      CONFIG_PCIE_CADENCE=y
+      CONFIG_PCIE_CADENCE_HOST=y
+
+   .. rubric:: **Compliance Mode**
+      :name: compliance-mode
+
+   In RC mode of operation, the Endpoint device can be forced to enter
+   Compliance Mode for PCIe compliance testing by setting the "EC" bit
+   in the LINK_CTRL_STATUS_2 register of the respective PCIe RC instance.
+   Setting "EC" to 1 initiates a hot reset thereby forcing the Endpoint
+   device into Compliance mode. The "EC" bit can be set from command-line
+   by using devmem2 utility as follows:
+
+      devmem2 <address> w <value>
+
+   where <address> is the address of LINK_CTRL_STATUS_2 register and
+   <value> is the resulting value to be written with "EC" bit of the
+   register set.
 
-        CONFIG_SOCIONEXT_SYNQUACER_PREITS=y
-        CONFIG_PCI=y
-        CONFIG_PCI_MSI=y
-        CONFIG_PCI_J721E=y
-        CONFIG_PCIE_CADENCE=y
-        CONFIG_PCIE_CADENCE_HOST=y
+   .. rubric:: **64-Bit Address Space with 4 GB Size**
+      :name: 64-bit-address-space
 
-    .. rubric:: **Compliance Mode**
-        :name: compliance-mode
+   The PCIe Controller support for 64-Bit addressing in the System's
+   Address Space with 4 GB Size is enabled in the device-tree.
+   The 4 GB region is split as:
 
-    In RC mode of operation, the Endpoint device can be forced to enter
-    Compliance Mode for PCIe compliance testing by setting the "EC" bit
-    in the LINK_CTRL_STATUS_2 register of the respective PCIe RC instance.
-    Setting "EC" to 1 initiates a hot reset thereby forcing the Endpoint
-    device into Compliance mode. The "EC" bit can be set from command-line
-    by using devmem2 utility as follows:
+   1. 4 KB ECAM region for Configuration Accesses
+   2. 1 MB IO region
+   3. Remaining region (4 GB - 1 MB - 4 KB) as 32-bit Non-Prefetchable MEM
 
-        devmem2 <address> w <value>
+   .. note::
 
-    where <address> is the address of LINK_CTRL_STATUS_2 register and
-    <value> is the resulting value to be written with "EC" bit of the
-    register set.
+      If the root complex is connected to an endpoint with virtual functions,
+      and the kernel panics during enumeration, add ``pci=realloc`` to ``optargs``
+      at the U-Boot prompt using the following command:
 
-    .. rubric:: **64-Bit Address Space with 4 GB Size**
-       :name: 64-bit-address-space
+      .. code-block:: console
 
-    The PCIe Controller support for 64-Bit addressing in the System's
-    Address Space with 4 GB Size is enabled in the device-tree.
-    The 4 GB region is split as:
+         setenv optargs 'pci=realloc'
 
-    1. 4 KB ECAM region for Configuration Accesses
-    2. 1 MB IO region
-    3. Remaining region (4 GB - 1 MB - 4 KB) as 32-bit Non-Prefetchable MEM
+      The ``pci=realloc`` parameter instructs the Linux kernel to reallocate PCI
+      bridge resources. This helps resolve resource conflicts during enumeration
+      of PCIe devices by allowing the kernel to reassign memory and I/O addresses.
 
-    .. rubric:: **Testing Details**
-       :name: testing-details
+   .. rubric:: **Testing Details**
+      :name: testing-details
 
-    The RC should enumerate any off-the-shelf PCIe cards. It has been tested
-    with Ethernet cards, NVMe cards, PCIe USB card, PCIe WiFi card, PCIe SATA
-    card and also to |__PART_FAMILY_DEVICE_NAMES__| in loopback mode.
+   The RC should enumerate any off-the-shelf PCIe cards. It has been tested
+   with Ethernet cards, NVMe cards, PCIe USB card, PCIe WiFi card, PCIe SATA
+   card and also to |__PART_FAMILY_DEVICE_NAMES__| in loopback mode.
 
-    In order to see if the connected card is detected, lspci utility should be
-    used. Different utilities can be used depending on the cards.
+   In order to see if the connected card is detected, lspci utility should be
+   used. Different utilities can be used depending on the cards.
 
-    Following are the outputs for some of them:
+   Following are the outputs for some of them:
 
-    - Loopback mode (|__PART_FAMILY_DEVICE_NAMES__| EVM to |__PART_FAMILY_DEVICE_NAMES__| EVM)
+   - Loopback mode (|__PART_FAMILY_DEVICE_NAMES__| EVM to |__PART_FAMILY_DEVICE_NAMES__| EVM)
 
       Two |__PART_FAMILY_DEVICE_NAMES__| EVMs can be connected in loopback mode by following
       the steps explained in