drm/sysfb: ofdrm: Add EDID support

Add EDID support to sysfb connector helpers. Read the EDID property
from the OF node in ofdrm. Without EDID, this does nothing.

Some systems with OF display, such as 32-bit PPC Macintoshs, provide
the system display's EDID data as node property in their DT. Exporting
this information allows compositors to implement correct DPI and
meaningful color management.

v3:
- avoid parser error by clearing EDID extension field
v2:
- return errno codes on errors (Jani)
- simplify EDID read logic (Jani)

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/gpu/drm/sysfb/drm_sysfb_helper.c

···
 #include <drm/drm_atomic_state_helper.h>
 #include <drm/drm_damage_helper.h>
 #include <drm/drm_drv.h>
+#include <drm/drm_edid.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_framebuffer.h>
 #include <drm/drm_gem_atomic_helper.h>
···
  * Connector
  */
 
+static int drm_sysfb_get_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
+{
+	struct drm_sysfb_device *sysfb = data;
+	const u8 *edid = sysfb->edid;
+	size_t off = block * EDID_LENGTH;
+	size_t end = off + len;
+
+	if (!edid)
+		return -EINVAL;
+	if (end > EDID_LENGTH)
+		return -EINVAL;
+	memcpy(buf, &edid[off], len);
+
+	/*
+	 * We don't have EDID extensions available and reporting them
+	 * will upset DRM helpers. Thus clear the extension field and
+	 * update the checksum. Adding the extension flag to the checksum
+	 * does this.
+	 */
+	buf[127] += buf[126];
+	buf[126] = 0;
+
+	return 0;
+}
+
 int drm_sysfb_connector_helper_get_modes(struct drm_connector *connector)
 {
 	struct drm_sysfb_device *sysfb = to_drm_sysfb_device(connector->dev);
+	const struct drm_edid *drm_edid;
 
+	if (sysfb->edid) {
+		drm_edid = drm_edid_read_custom(connector, drm_sysfb_get_edid_block, sysfb);
+		drm_edid_connector_update(connector, drm_edid);
+		drm_edid_free(drm_edid);
+	}
+
+	/* Return the fixed mode even with EDID */
 	return drm_connector_helper_get_modes_fixed(connector, &sysfb->fb_mode);
 }
 EXPORT_SYMBOL(drm_sysfb_connector_helper_get_modes);

drivers/gpu/drm/sysfb/drm_sysfb_helper.h

···
 struct drm_sysfb_device {
 	struct drm_device dev;
 
+	const u8 *edid; /* can be NULL */
+
 	/* hardware settings */
 	struct drm_display_mode fb_mode;
 	const struct drm_format_info *fb_format;

drivers/gpu/drm/sysfb/ofdrm.c

···
 #include <drm/drm_damage_helper.h>
 #include <drm/drm_device.h>
 #include <drm/drm_drv.h>
+#include <drm/drm_edid.h>
 #include <drm/drm_fbdev_shmem.h>
 #include <drm/drm_format_helper.h>
 #include <drm/drm_framebuffer.h>
···
 	return address;
 }
 
+static const u8 *display_get_edid_of(struct drm_device *dev, struct device_node *of_node,
+				     u8 buf[EDID_LENGTH])
+{
+	int ret = of_property_read_u8_array(of_node, "EDID", buf, EDID_LENGTH);
+
+	if (ret)
+		return NULL;
+	return buf;
+}
+
 static bool is_avivo(u32 vendor, u32 device)
 {
 	/* This will match most R5xx */
···
 
 	/* colormap */
 	void __iomem *cmap_base;
+
+	u8 edid[EDID_LENGTH];
 
 	/* modesetting */
 	u32 formats[DRM_SYSFB_PLANE_NFORMATS(1)];
···
 	int width, height, depth, linebytes;
 	const struct drm_format_info *format;
 	u64 address;
+	const u8 *edid;
 	resource_size_t fb_size, fb_base, fb_pgbase, fb_pgsize;
 	struct resource *res, *mem;
 	void __iomem *screen_base;
···
 		}
 	}
 
+	/* EDID is optional */
+	edid = display_get_edid_of(dev, of_node, odev->edid);
+
 	/*
 	 * Firmware framebuffer
 	 */
···
 	sysfb->fb_pitch = linebytes;
 	if (odev->cmap_base)
 		sysfb->fb_gamma_lut_size = OFDRM_GAMMA_LUT_SIZE;
+	sysfb->edid = edid;
 
 	drm_dbg(dev, "display mode={" DRM_MODE_FMT "}\n", DRM_MODE_ARG(&sysfb->fb_mode));
 	drm_dbg(dev, "framebuffer format=%p4cc, size=%dx%d, linebytes=%d byte\n",
···
 	drm_connector_set_panel_orientation_with_quirk(connector,
 						       DRM_MODE_PANEL_ORIENTATION_UNKNOWN,
 						       width, height);
+	if (edid)
+		drm_connector_attach_edid_property(connector);
 
 	ret = drm_connector_attach_encoder(connector, encoder);
 	if (ret)