On Wed, 2022-07-27 at 10:41 +0200, Thomas Zimmermann wrote:

quoted

quoted

+static void __iomem *ofdrm_mach64_cmap_ioremap(struct ofdrm_device *odev,
+					       struct device_node *of_node,
+					       u64 fb_base)
+{
+	struct drm_device *dev = &odev->dev;
+	u64 address;
+	void __iomem *cmap_base;
+
+	address = fb_base & 0xff000000ul;
+	address += 0x7ff000;
+

It would be good to know where these addresses are coming from. Maybe some
constant macros or a comment ? Same for the other places where addresses
and offsets are used.

I have no idea where these values come from. I took them from offb. And 
I suspect that some of these CMAP helpers could be further merged if 
only it was clear where the numbers come from.  But as i don't have the 
equipment for testing, I took most of this literally as-is from offb.

Ancient black magic :-) Old ATI mach64 chips had the registers sitting
at the end of the framebuffer. You can find an equivalent in
drivers/video/aty/atyfb_base.c:atyfb_setup_generic():

	raddr = addr + 0x7ff000UL;

Cheers,
Ben.