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authorBenjamin Herrenschmidt <benh@kernel.crashing.org>2013-07-25 12:12:32 +1000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2013-08-14 14:57:40 +1000
commit7191b615759ec10cab9eea43be5ecc42cda82364 (patch)
tree48e96713113f5c8a54a7021d0dd5bc6b31d32f15 /arch/powerpc/kernel/setup_64.c
parent1a85d66bcc90e2cbdf04f70d6586b82532142e85 (diff)
powerpc/pmac: Early debug output on screen on 64-bit macs
We have a bunch of CONFIG_PPC_EARLY_DEBUG_* options that are intended for bringup/debug only. They hard wire a machine specific udbg backend very early on (before we even probe the platform), and use whatever tricks are available on each machine/cpu to be able to get some kind of output out there early on. So far, on powermac with no serial ports, we have CONFIG_PPC_EARLY_DEBUG_BOOTX to use the low-level btext engine on the screen, but it doesn't do much, at least on 64-bit. It only really gets enabled after the platform has been probed and the MMU enabled. This adds a way to enable it much earlier. From prom_init.c (while still running with Open Firmware), we grab the screen details and set things up using the physical address of the frame buffer. Then btext itself uses the "rm_ci" feature of the 970 processor (Real Mode Cache Inhibited) to access it while in real mode. We need to do a little bit of reorg of the btext code to inline things better, in order to limit how much we touch memory while in this mode as the consequences might be ... interesting. This successfully allowed me to debug problems early on with the G5 (related to gold being broken vs. ppc64 kernels). Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/kernel/setup_64.c')
-rw-r--r--arch/powerpc/kernel/setup_64.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 79ba9b77fe72..0c0450dd4d31 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -10,7 +10,7 @@
* 2 of the License, or (at your option) any later version.
*/
-#undef DEBUG
+#define DEBUG
#include <linux/export.h>
#include <linux/string.h>
@@ -240,6 +240,18 @@ void __init early_setup(unsigned long dt_ptr)
reserve_hugetlb_gpages();
DBG(" <- early_setup()\n");
+
+#ifdef CONFIG_PPC_EARLY_DEBUG_BOOTX
+ /*
+ * This needs to be done *last* (after the above DBG() even)
+ *
+ * Right after we return from this function, we turn on the MMU
+ * which means the real-mode access trick that btext does will
+ * no longer work, it needs to switch to using a real MMU
+ * mapping. This call will ensure that it does
+ */
+ btext_map();
+#endif /* CONFIG_PPC_EARLY_DEBUG_BOOTX */
}
#ifdef CONFIG_SMP