Note lack of display output on kernels older than 6.15

Latest device tree changes have broken the partial HDMI0 support on
kernels < 6.15 for boards exposing the HDMI1 port.

The "Force UEFI GOP Display" option must be used instead with those
older kernels.

Signed-off-by: Mario Bălănică <mariobalanica02@gmail.com>

Author: mariobalanica

README.md

@@ -69,7 +69,7 @@ Note that this list is subject to change at any time as devices gain better supp
 ### Mainline compatibility mode
 | OS | Version | Tested/supported hardware | Notes |
 | --- | --- | --- | --- |
-| Generic upstream Linux | Kernel 6.10 or newer.<br> Tested with:<br> - Ubuntu 24.10<br> - Fedora Workstation 41<br> - Fedora Workstation Rawhide | Platform and kernel version dependent, see [Collabora's RK3588 upstream status](https://gitlab.collabora.com/hardware-enablement/rockchip-3588/notes-for-rockchip-3588/-/blob/main/mainline-status.md). | * Kernels older than 6.13 lack HDMI output. To work around this, see: [Device Tree configuration](#device-tree-configuration). |
+| Generic upstream Linux | Kernel 6.10 or newer.<br> Tested with:<br> - Ubuntu 24.10<br> - Fedora Workstation 41<br> - Fedora Workstation Rawhide | Platform and kernel version dependent, see [Collabora's RK3588 upstream status](https://gitlab.collabora.com/hardware-enablement/rockchip-3588/notes-for-rockchip-3588/-/blob/main/mainline-status.md). | * Kernels older than 6.15 lack display output. To work around this, see: [Device Tree configuration](#device-tree-configuration). |
 
 > [!NOTE]
 > Mainline support is only available on [Platinum](#platinum) platforms.
@@ -171,7 +171,7 @@ The firmware provides two compatibility modes:
 [Platinum](#platinum) platforms will have the `Mainline` option enabled by default, while [Bronze](#bronze) ones will fall back to `Vendor`.
 
 > [!TIP]
-> In `Mainline` mode with generic Linux kernels older than 6.13, the HDMI output will not be usable. To use the UEFI-initialized display instead, go to `Device Manager`->`Rockchip Platform Configuration`->`ACPI / Device Tree` and enable `Force UEFI GOP Display`. Note that GPU acceleration cannot work in this mode.
+> In `Mainline` mode with generic Linux kernels older than 6.15, the HDMI output will not be usable. To use the UEFI-initialized display instead, go to `Device Manager`->`Rockchip Platform Configuration`->`ACPI / Device Tree` and enable `Force UEFI GOP Display`. Note that GPU acceleration cannot work in this mode.
 
 ### Custom Device Tree Blob (DTB) override and overlays
 It is also possible to provide a custom DTB and overlays. To enable this, go to `Device Manager`->`Rockchip Platform Configuration`->`ACPI / Device Tree` and set `Support DTB override & overlays` to `Enabled`.

edk2-rockchip/Silicon/Rockchip/RK3588/Drivers/RK3588Dxe/RK3588DxeHii.uni

@@ -258,7 +258,7 @@
 #string STR_FDT_COMPAT_MODE_MAINLINE                       #language en-US "Mainline"
 
 #string STR_FDT_FORCE_GOP_PROMPT                           #language en-US "Force UEFI GOP Display"
-#string STR_FDT_FORCE_GOP_HELP                             #language en-US "This option allows using the basic display output provided by UEFI GOP (HDMI/DP/DSI) on Linux kernels older than 6.13, which lack native driver support."
+#string STR_FDT_FORCE_GOP_HELP                             #language en-US "This option allows using the basic display output provided by UEFI GOP (HDMI/DP/DSI) on older Linux kernels, which lack native driver support."
 
 #string STR_FDT_SUPPORT_OVERRIDES_PROMPT                   #language en-US "Support DTB override & overlays"
 #string STR_FDT_SUPPORT_OVERRIDES_HELP                     #language en-US "Enable or disable support for overriding the firmware-provided DTB and installing overlays.\n\nCheck firmware documentation for more details."