Re: drm/mgag200: Fix big-endian support

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 26.08.26 um 19:30 schrieb Christian Zigotzky:
> On 26 August 2026 at 05:23 pm, Thomas Zimmermann <tzimmermann@suse.de> wrote:
>
> Hi
>
> Could be that we have to enable access to the ROM first. That's why it returns only 0xffff. Does the card display output when you switch on the computer?
>
> Best regards
> Thomas
>
> - - -
>
> Hello Thomas,
>
> No, the card doesn’t display output when I switch on the computer.

Attached you'll find another patch that also enables ROM access in the 
PCI config options.  I took the code out of the old matroxfb driver 
without further testing. Please try and report back on the results.

Best regards
Thomas



>
> Cheers,
> Christian

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)


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From 101ee2c18a64101978091006b797a7c327d295ff Mon Sep 17 00:00:00 2001
From: Thomas Zimmermann <tzimmermann@suse.de>
Date: Wed, 26 Aug 2026 11:03:11 +0200
Subject: [PATCH] [v2] mgag200: go looking for PInS in the video BIOS ROM on
 non-x86

---
 drivers/gpu/drm/mgag200/mgag200_g200.c | 38 ++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/mgag200/mgag200_g200.c b/drivers/gpu/drm/mgag200/mgag200_g200.c
index 9e6b4618fadd..57f87dfd26ec 100644
--- a/drivers/gpu/drm/mgag200/mgag200_g200.c
+++ b/drivers/gpu/drm/mgag200/mgag200_g200.c
@@ -239,7 +239,7 @@ static void mgag200_g200_interpret_bios(struct mgag200_g200_device *g200,
 	};
 	struct mga_device *mdev = &g200->base;
 	struct drm_device *dev = &mdev->base;
-	const unsigned char *pins;
+	const unsigned char *pins = NULL;
 	unsigned int pins_len, version;
 	int offset;
 	int tmp;
@@ -250,16 +250,34 @@ static void mgag200_g200_interpret_bios(struct mgag200_g200_device *g200,
 	if (memcmp(&bios[45], matrox, sizeof(matrox)) != 0)
 		return;
 
+#if defined(CONFIG_X86)
 	/* Get the PInS offset. */
 	if (size < MGA_BIOS_OFFSET + 2)
 		return;
 	offset = (bios[MGA_BIOS_OFFSET + 1] << 8) | bios[MGA_BIOS_OFFSET];
+	if (size < offset + 6)
+		return;
 
 	/* Get PInS data structure. */
+	pins = bios + offset;
+#else
+	/*
+	 * On OpenFirmware systems (PPC, MIPS, SPARC) the offset isn't stored
+	 * at the end of the BIOS image. Look for the PInS header instead.
+	 */
+	for (offset = 0 ; offset < size - 6; ++offset) {
+		const unsigned char *buf = bios + offset;
+
+		if (buf[0] == 0x2e && buf[1] == 0x41 && ((buf[2] == 64) || (buf[2] == 128))) {
+			pins = buf;
+			break;
+		}
+	}
 
-	if (size < offset + 6)
+	if (!pins)
 		return;
-	pins = bios + offset;
+#endif
+
 	if (pins[0] == 0x2e && pins[1] == 0x41) {
 		version = pins[5];
 		pins_len = pins[2];
@@ -320,6 +338,8 @@ static void mgag200_g200_interpret_bios(struct mgag200_g200_device *g200,
 	}
 }
 
+#define PCI_MGA_OPTION_BIOSEN 0x40000000
+
 static void mgag200_g200_init_refclk(struct mgag200_g200_device *g200)
 {
 	struct mga_device *mdev = &g200->base;
@@ -328,11 +348,20 @@ static void mgag200_g200_init_refclk(struct mgag200_g200_device *g200)
 	unsigned char __iomem *rom;
 	unsigned char *bios;
 	size_t size;
+	u32 opt;
+	u32 biosbase;
+	u32 fbbase;
 
 	g200->pclk_min = 50000;
 	g200->pclk_max = 230000;
 	g200->ref_clk = 27050;
 
+	pci_read_config_dword(pdev, PCI_MGA_OPTION, &opt);
+	pci_write_config_dword(pdev, PCI_MGA_OPTION, opt | PCI_MGA_OPTION_BIOSEN);
+	pci_read_config_dword(pdev, PCI_ROM_ADDRESS, &biosbase);
+	pci_read_config_dword(pdev, PCI_BASE_ADDRESS_0, &fbbase);
+	pci_write_config_dword(pdev, PCI_ROM_ADDRESS, (fbbase & PCI_ROM_ADDRESS_MASK) | PCI_ROM_ADDRESS_ENABLE);
+
 	rom = pci_map_rom(pdev, &size);
 	if (!rom)
 		return;
@@ -351,6 +380,9 @@ static void mgag200_g200_init_refclk(struct mgag200_g200_device *g200)
 	vfree(bios);
 out:
 	pci_unmap_rom(pdev, rom);
+
+	pci_write_config_dword(pdev, PCI_ROM_ADDRESS, biosbase);
+	pci_write_config_dword(pdev, PCI_MGA_OPTION, opt);
 }
 
 static const struct mgag200_device_funcs mgag200_g200_device_funcs = {
-- 
2.55.0