[PATCH v3 4/6] LoongArch: video: Implement primary framebuffer device detection

[wuqianhai]

From: wuqianhai <wuqianhai@xxxxxxxxxxx>

The LoongArch port does not implement video_is_primary_device(), so it
falls back to the generic stub that always returns false.  As a result,
with CONFIG_FRAMEBUFFER_CONSOLE_DETECT_PRIMARY=y the framebuffer console
cannot map itself to the primary display device and instead binds to the
first registered framebuffer, which is not necessarily the one the
firmware used for the boot console.

Implement video_is_primary_device() by returning whether the device is
the VGA default device.  This reuses the VGA arbiter's choice instead of
matching the firmware framebuffer by address, so it is stable across BAR
resizing: the default device is fixed before any driver runs.

Signed-off-by: wuqianhai <wuqianhai@xxxxxxxxxxx>
---
 arch/loongarch/Makefile             |  3 +++
 arch/loongarch/include/asm/video.h  |  7 +++++++
 arch/loongarch/video/Makefile       |  3 +++
 arch/loongarch/video/video-common.c | 29 +++++++++++++++++++++++++++++
 4 files changed, 42 insertions(+)
 create mode 100644 arch/loongarch/video/Makefile
 create mode 100644 arch/loongarch/video/video-common.c

diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index 4b22f95aaafb..7fca93298cef 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -166,6 +166,9 @@ bootvars-y	= VMLINUX_LOAD_ADDRESS=$(load-y)
 
 drivers-$(CONFIG_PCI)		+= arch/loongarch/pci/
 
+# framebuffer console primary device detection
+drivers-$(CONFIG_VIDEO)		+= arch/loongarch/video/
+
 KBUILD_AFLAGS	+= $(cflags-y)
 KBUILD_CFLAGS	+= $(cflags-y)
 KBUILD_CPPFLAGS += -DVMLINUX_LOAD_ADDRESS=$(load-y)
diff --git a/arch/loongarch/include/asm/video.h b/arch/loongarch/include/asm/video.h
index 9f76845f2d4f..7b38881ea1d6 100644
--- a/arch/loongarch/include/asm/video.h
+++ b/arch/loongarch/include/asm/video.h
@@ -8,6 +8,13 @@
 #include <linux/compiler.h>
 #include <linux/string.h>
 
+struct device;
+
+#ifdef CONFIG_VIDEO
+bool video_is_primary_device(struct device *dev);
+#define video_is_primary_device video_is_primary_device
+#endif
+
 static inline void fb_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
 {
 	memcpy(to, (void __force *)from, n);
diff --git a/arch/loongarch/video/Makefile b/arch/loongarch/video/Makefile
new file mode 100644
index 000000000000..f1b2a7e54033
--- /dev/null
+++ b/arch/loongarch/video/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-$(CONFIG_VIDEO)		+= video-common.o
diff --git a/arch/loongarch/video/video-common.c b/arch/loongarch/video/video-common.c
new file mode 100644
index 000000000000..6fea46661cb6
--- /dev/null
+++ b/arch/loongarch/video/video-common.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2026 Loongson Technology Corporation Limited
+ */
+
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/vgaarb.h>
+
+#include <asm/video.h>
+
+bool video_is_primary_device(struct device *dev)
+{
+	struct pci_dev *pdev;
+
+	if (!dev_is_pci(dev))
+		return false;
+
+	pdev = to_pci_dev(dev);
+
+	if (!pci_is_display(pdev))
+		return false;
+
+	return pdev == vga_default_device();
+}
+EXPORT_SYMBOL(video_is_primary_device);
+
+MODULE_DESCRIPTION("LoongArch video helpers");
+MODULE_LICENSE("GPL");
-- 
2.34.1