drm/aspeed: Add sysfs for output settings

These settings are used by an ASPEED BMC to determine when the host is
trying to drive the display over PCIe (vga_pw) and to switch the
output between PCIe and the internal graphics device (dac_mux).

The valid values for the dac mux are:

 00: VGA mode (default, aka PCIe)
 01: Graphics CRT (aka BMC internal graphics, this driver)
 10: Pass through mode from video input port A
 11: Pass through mode from video input port B

Values for the read-only vga password register are:

 1: Host driving the display
 0: Host not driving the display
Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://patchwork.freedesktop.org/patch/msgid/20200916083413.777307-1-joel@jms.id.au

drivers/gpu/drm/aspeed/aspeed_gfx_drv.c

@@ -212,6 +212,69 @@ static const struct of_device_id aspeed_gfx_match[] = {
 	{ }
 };
 
+#define ASPEED_SCU_VGA0		0x50
+#define ASPEED_SCU_MISC_CTRL	0x2c
+
+static ssize_t dac_mux_store(struct device *dev, struct device_attribute *attr,
+			     const char *buf, size_t count)
+{
+	struct aspeed_gfx *priv = dev_get_drvdata(dev);
+	u32 val;
+	int rc;
+
+	rc = kstrtou32(buf, 0, &val);
+	if (rc)
+		return rc;
+
+	if (val > 3)
+		return -EINVAL;
+
+	rc = regmap_update_bits(priv->scu, ASPEED_SCU_MISC_CTRL, 0x30000, val << 16);
+	if (rc < 0)
+		return 0;
+
+	return count;
+}
+
+static ssize_t dac_mux_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct aspeed_gfx *priv = dev_get_drvdata(dev);
+	u32 reg;
+	int rc;
+
+	rc = regmap_read(priv->scu, ASPEED_SCU_MISC_CTRL, &reg);
+	if (rc)
+		return rc;
+
+	return sprintf(buf, "%u\n", (reg >> 16) & 0x3);
+}
+static DEVICE_ATTR_RW(dac_mux);
+
+static ssize_t
+vga_pw_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct aspeed_gfx *priv = dev_get_drvdata(dev);
+	u32 reg;
+	int rc;
+
+	rc = regmap_read(priv->scu, ASPEED_SCU_VGA0, &reg);
+	if (rc)
+		return rc;
+
+	return sprintf(buf, "%u\n", reg & 1);
+}
+static DEVICE_ATTR_RO(vga_pw);
+
+static struct attribute *aspeed_sysfs_entries[] = {
+	&dev_attr_vga_pw.attr,
+	&dev_attr_dac_mux.attr,
+	NULL,
+};
+
+static struct attribute_group aspeed_sysfs_attr_group = {
+	.attrs = aspeed_sysfs_entries,
+};
+
 static int aspeed_gfx_probe(struct platform_device *pdev)
 {
 	struct aspeed_gfx *priv;
@@ -226,6 +289,12 @@ static int aspeed_gfx_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	dev_set_drvdata(&pdev->dev, priv);
+
+	ret = sysfs_create_group(&pdev->dev.kobj, &aspeed_sysfs_attr_group);
+	if (ret)
+		return ret;
+
 	ret = drm_dev_register(&priv->drm, 0);
 	if (ret)
 		goto err_unload;
@@ -234,6 +303,7 @@ static int aspeed_gfx_probe(struct platform_device *pdev)
 	return 0;
 
 err_unload:
+	sysfs_remove_group(&pdev->dev.kobj, &aspeed_sysfs_attr_group);
 	aspeed_gfx_unload(&priv->drm);
 
 	return ret;
@@ -243,6 +313,7 @@ static int aspeed_gfx_remove(struct platform_device *pdev)
 {
 	struct drm_device *drm = platform_get_drvdata(pdev);
 
+	sysfs_remove_group(&pdev->dev.kobj, &aspeed_sysfs_attr_group);
 	drm_dev_unregister(drm);
 	aspeed_gfx_unload(drm);