drm/ast: Set PCI config before accessing I/O registers

Access to I/O registers is required to detect and set up the
device. Enable the rsp PCI config bits before. While at it,
convert the magic number to macro constants.

Enabling the PCI config bits was done after trying to detect
the device. It was probably too late at this point.

v2:
	* use standard 16-bit PCI r/w access (Jingfeng)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com> # AST2600
Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20230621130032.3568-7-tzimmermann@suse.de

drivers/gpu/drm/ast/ast_drv.h

@@ -52,7 +52,6 @@
 #define PCI_CHIP_AST2000 0x2000
 #define PCI_CHIP_AST2100 0x2010
 
-
 enum ast_chip {
 	AST2000,
 	AST2100,

drivers/gpu/drm/ast/ast_main.c

@@ -35,6 +35,23 @@
 
 #include "ast_drv.h"
 
+static int ast_init_pci_config(struct pci_dev *pdev)
+{
+	int err;
+	u16 pcis04;
+
+	err = pci_read_config_word(pdev, PCI_COMMAND, &pcis04);
+	if (err)
+		goto out;
+
+	pcis04 |= PCI_COMMAND_MEMORY | PCI_COMMAND_IO;
+
+	err = pci_write_config_word(pdev, PCI_COMMAND, pcis04);
+
+out:
+	return pcibios_err_to_errno(err);
+}
+
 static void ast_detect_config_mode(struct drm_device *dev, u32 *scu_rev)
 {
 	struct device_node *np = dev->dev->of_node;
@@ -399,6 +416,10 @@ struct ast_device *ast_device_create(const struct drm_driver *drv,
 			return ERR_PTR(-EIO);
 	}
 
+	ret = ast_init_pci_config(pdev);
+	if (ret)
+		return ERR_PTR(ret);
+
 	if (!ast_is_vga_enabled(dev)) {
 		drm_info(dev, "VGA not enabled on entry, requesting chip POST\n");
 		need_post = true;

drivers/gpu/drm/ast/ast_post.c

@@ -361,12 +361,6 @@ static void ast_init_dram_reg(struct drm_device *dev)
 void ast_post_gpu(struct drm_device *dev)
 {
 	struct ast_device *ast = to_ast_device(dev);
-	struct pci_dev *pdev = to_pci_dev(dev->dev);
-	u32 reg;
-
-	pci_read_config_dword(pdev, 0x04, &reg);
-	reg |= 0x3;
-	pci_write_config_dword(pdev, 0x04, reg);
 
 	ast_enable_vga(dev);
 	ast_open_key(ast);