NVIDIA: SAUCE: MEDIATEK: platform: Add PCIe Hotplug Driver for CX7 on DGX Spark

BugLink: https://bugs.launchpad.net/bugs/2138269

This driver manages PCIe link for NVIDIA ConnectX-7 (CX7) hot-plug/unplug
on DGX Spark systems with GB10 SoC. It disables the PCIe link
on cable removal and enables it on cable insertion.

Upstream-friendly improvements over 6.14 driver:
- Separated from MTK pinctrl driver into NVIDIA platform driver
- Configuration via ACPI (_CRS and _DSD), no hardcoded values
- Device-managed resources (devm_*) for automatic cleanup
- Thread-safe state management with locking
- Enhanced error handling and logging
- Uses standard Linux kernel APIs

The driver exposes a sysfs interface to emulate cable plug in/out:
  echo 1 > /sys/devices/platform/MTKP0001:00/pcie_hotplug/debug_state  # plug in
  echo 0 > /sys/devices/platform/MTKP0001:00/pcie_hotplug/debug_state  # plug out

It also provides a runtime enable/disable switch via sysfs:
  echo 1 > /sys/devices/platform/MTKP0001:00/pcie_hotplug/hotplug_enabled  # Enable
  echo 0 > /sys/devices/platform/MTKP0001:00/pcie_hotplug/hotplug_enabled  # Disable

This allows enabling/disabling hotplug functionality. Hotplug is disabled by default
and must be explicitly enabled via userspace.

It also implements uevent notifications for coordination with userspace:

* cable plug-in:
    Report plug-in uevent (driver)
    Enable PCIe link (driver)
    Rescan CX7 devices (application)

* cable removal:
    Report removal uevent (driver)
    Remove CX7 devices (application)
    Disable PCIe link (driver)

Signed-off-by: Vaibhav Vyas <vavyas@nvidia.com>
Signed-off-by: Scott Fudally <sfudally@nvidia.com>
Signed-off-by: Surabhi Chythanya Kumar <schythanyaku@nvidia.com>
Acked-by: Jamie Nguyen <jamien@nvidia.com>
Acked-by: Carol L Soto <csoto@nvidia.com>
Acked-by: Noah Wager <noah.wager@canonical.com>
Acked-by: Jacob Martin <jacob.martin@canonical.com>
Signed-off-by: Brad Figg <bfigg@nvidia.com>

Author: schythanyaku

debian.nvidia-6.17/config/annotations

@@ -141,6 +141,9 @@ CONFIG_MICROSOFT_MANA                           note<'LP: #2084598'>
 CONFIG_MTD                                      policy<{'amd64': 'm', 'arm64': 'y'}>
 CONFIG_MTD                                      note<'Essential for boot on ARM64'>
 
+CONFIG_MTK_PCIE_HOTPLUG                         policy<{'arm64': 'm'}>
+CONFIG_MTK_PCIE_HOTPLUG                         note<'CX7 PCIe hotplug driver for NVIDIA DGX Spark systems with GB10 SoC.'>
+
 CONFIG_NOUVEAU_DEBUG                            policy<{'amd64': '-', 'arm64': '-'}>
 CONFIG_NOUVEAU_DEBUG                            note<'Disable nouveau for NVIDIA kernels'>
 

drivers/platform/arm64/Kconfig

@@ -95,4 +95,6 @@ config NVIDIA_FFA_EC
 
 	 Say M or Y here to include this support.
 
+source "drivers/platform/arm64/nvidia/Kconfig"
+
 endif # ARM64_PLATFORM_DEVICES

drivers/platform/arm64/Makefile

@@ -10,3 +10,4 @@ obj-$(CONFIG_EC_HUAWEI_GAOKUN)	+= huawei-gaokun-ec.o
 obj-$(CONFIG_EC_LENOVO_YOGA_C630) += lenovo-yoga-c630.o
 obj-$(CONFIG_EC_LENOVO_YOGA_SLIM7X) += lenovo-yoga-slim7x.o
 obj-$(CONFIG_NVIDIA_FFA_EC) += nvidia-ffa-ec.o
+obj-y += nvidia/

drivers/platform/arm64/nvidia/Kconfig

@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# NVIDIA ARM64 Platform-Specific Device Drivers
+#
+
+config MTK_PCIE_HOTPLUG
+	tristate "CX7 PCIe Hotplug Driver"
+	depends on EINT_MTK
+	depends on PCI && ACPI
+	help
+	  Say Y here to support PCIe device plug in/out detection.
+	  It will disable PCIe link when plug out and enable
+	  PCIe link after plug in.
+
+	  This is particularly useful for GB10 SoC.
+
+	  If unsure, say N.

drivers/platform/arm64/nvidia/Makefile

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for NVIDIA ARM64 platform-specific drivers
+#
+# CX7 PCIe Hotplug Driver
+# Provides hotplug support for CX7 PCIe devices on GB10 SoC-based systems
+#
+
+obj-$(CONFIG_MTK_PCIE_HOTPLUG) += mtk-pcie-hotplug.o