svn commit: r333897 - head/sys/dev/vt/hw/ofwfb

[Nathan Whitehorn]

Author: nwhitehorn
Date: Sat May 19 22:04:54 2018
New Revision: 333897
URL: https://svnweb.freebsd.org/changeset/base/333897

Log:
  Avoid writing to the frame buffer in early boot on PowerPC if the CPU's
  MMU is disabled.
  
  This expands some earlier logic and avoids a number of potential problems:
  1. The CPU may not be able to access the framebuffer in real mode (real
     mode does not necessarily encompass all available memory, especially
     under a hypervisor).
  2. Real mode accesses generally assume cacheability, so it might not
     even have worked.
  3. The difference in cacheability between real mode and later (and
     potentially earlier) points in the boot with the MMU on may cause
     ERAT parity problems, resulting in a machine check.
  
  This fixes real-mode (usefdt=1) early boot on the G5 iMac, which was
  previously broken as a result of issue #3. Late boot will require some
  other fixups.

Modified:
  head/sys/dev/vt/hw/ofwfb/ofwfb.c

Modified: head/sys/dev/vt/hw/ofwfb/ofwfb.c
==============================================================================
--- head/sys/dev/vt/hw/ofwfb/ofwfb.c	Sat May 19 21:36:55 2018	(r333896)
+++ head/sys/dev/vt/hw/ofwfb/ofwfb.c	Sat May 19 22:04:54 2018	(r333897)
@@ -45,6 +45,7 @@ __FBSDID("$FreeBSD$");
 #ifdef __sparc64__
 #include <machine/bus_private.h>
 #endif
+#include <machine/cpu.h>
 
 #include <dev/ofw/openfirm.h>
 #include <dev/ofw/ofw_bus.h>
@@ -138,6 +139,7 @@ ofwfb_bitblt_bitmap(struct vt_device *vd, const struct
 		if (pmap_bootstrapped) {
 			sc->fb_flags &= ~FB_FLAG_NOWRITE;
 			ofwfb_initialize(vd);
+			vd->vd_driver->vd_blank(vd, TC_BLACK);
 		} else {
 			return;
 		}
@@ -490,11 +492,6 @@ ofwfb_init(struct vt_device *vd)
 		OF_decode_addr(node, fb_phys, &sc->sc_memt, &sc->fb.fb_vbase,
 		    NULL);
 		sc->fb.fb_pbase = sc->fb.fb_vbase & ~DMAP_BASE_ADDRESS;
-		#ifdef __powerpc64__
-		/* Real mode under a hypervisor probably doesn't cover FB */
-		if (!(mfmsr() & (PSL_HV | PSL_DR)))
-			sc->fb.fb_flags |= FB_FLAG_NOWRITE;
-		#endif
 	#else
 		/* No ability to interpret assigned-addresses otherwise */
 		return (CN_DEAD);
@@ -502,6 +499,17 @@ ofwfb_init(struct vt_device *vd)
         }
 
 
+	#if defined(__powerpc__)
+	/*
+	 * If we are running on PowerPC in real mode (supported only on AIM
+	 * CPUs), the frame buffer may be inaccessible (real mode does not
+	 * necessarily cover all RAM) and may also be mapped with the wrong
+	 * cache properties (all real mode accesses are assumed cacheable).
+	 * Just don't write to it for the time being.
+	 */
+	if (!(cpu_features & PPC_FEATURE_BOOKE) && !(mfmsr() & PSL_DR))
+		sc->fb.fb_flags |= FB_FLAG_NOWRITE;
+	#endif
 	ofwfb_initialize(vd);
 	vt_fb_init(vd);