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powerpc/pmac: Early debug output on screen on 64-bit macs

PATCH In review Benjamin Herrenschmidt 2 participants 4 messages Jul 25, 2013 – Sep 13, 2013 PowerPC

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Benjamin Herrenschmidt

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PATCH 1/1 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 <[email protected]>

---

arch/powerpc/include/asm/btext.h +1 -0
index 906f46e..89fc382 100644
@@ -13,6 +13,7 @@ extern void btext_update_display(unsigned long phys, int width, int height,
 extern void btext_setup_display(int width, int height, int depth, int pitch,
 				unsigned long address);
 extern void btext_prepare_BAT(void);
+extern void btext_map(void);
 extern void btext_unmap(void);
 
 extern void btext_drawchar(char c);
arch/powerpc/kernel/btext.c +139 -115

321 lines not on this page · raw message

arch/powerpc/kernel/misc_64.S +31 -0
index 6820e45..5a29bc5 100644
@@ -247,6 +247,37 @@ _GLOBAL(__bswapdi2)
 	blr
 
 #if defined(CONFIG_PPC_PMAC) || defined(CONFIG_PPC_MAPLE)
+
+_GLOBAL(rmci_on)
+	sync
+	isync
+	li	r3,0x100
+	rldicl	r3,r3,32,0
+	mfspr	r5,SPRN_HID4
+	or	r5,r5,r3
+	sync
+	mtspr	SPRN_HID4,r5
+	isync
+	slbia
+	isync
+	sync
+	blr
+
+_GLOBAL(rmci_off)
+	sync
+	isync
+	li	r3,0x100
+	rldicl	r3,r3,32,0
+	mfspr	r5,SPRN_HID4
+	andc	r5,r5,r3
+	sync
+	mtspr	SPRN_HID4,r5
+	isync
+	slbia
+	isync
+	sync
+	blr
+
 /*
  * Do an IO access in real mode
  */
arch/powerpc/kernel/prom_init.c +16 -0
index 6079024..57df5cb 100644
@@ -2082,6 +2082,22 @@ static void __init prom_check_displays(void)
 					   clut[2]) != 0)
 				break;
 #endif /* CONFIG_LOGO_LINUX_CLUT224 */
+
+#ifdef CONFIG_PPC_EARLY_DEBUG_BOOTX
+		if (prom_getprop(node, "linux,boot-display", NULL, 0) !=
+		    PROM_ERROR) {
+			u32 width, height, pitch, addr;
+
+			prom_printf("Setting btext !\n");
+			prom_getprop(node, "width", &width, 4);
+			prom_getprop(node, "height", &height, 4);
+			prom_getprop(node, "linebytes", &pitch, 4);
+			prom_getprop(node, "address", &addr, 4);
+			prom_printf("W=%d H=%d LB=%d addr=0x%x\n",
+				    width, height, pitch, addr);
+			btext_setup_display(width, height, 8, pitch, addr);
+		}
+#endif /* CONFIG_PPC_EARLY_DEBUG_BOOTX */
 	}
 }
arch/powerpc/kernel/prom_init_check.sh +2 -1
index 3765da6..b0c263d 100644
@@ -22,7 +22,8 @@ __secondary_hold_acknowledge __secondary_hold_spinloop __start
 strcmp strcpy strlcpy strlen strncmp strstr logo_linux_clut224
 reloc_got2 kernstart_addr memstart_addr linux_banner _stext
 opal_query_takeover opal_do_takeover opal_enter_rtas opal_secondary_entry
-boot_command_line __prom_init_toc_start __prom_init_toc_end"
+boot_command_line __prom_init_toc_start __prom_init_toc_end
+btext_setup_display"
 
 NM="$1"
 OBJ="$2"
arch/powerpc/kernel/setup_64.c +13 -1
index 389fb807..7016a13 100644
@@ -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>

@@ -237,6 +237,18 @@ 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
author
#1 lore raw

arch/powerpc/kernel/setup_64.c line 13

Quoted 8 lines · Benjamin Herrenschmidt
arch/powerpc/kernel/setup_64.c +1 -1
@@ -10,7 +10,7 @@
  *      2 of the License, or (at your option) any later version.
  */
 
-#undef DEBUG
+#define DEBUG

Ooops... sent the wrong version. Will send an updated one later, if there are no other comments.

Cheers,
Ben.

#2 lore raw
Quoted 7 lines · Benjamin Herrenschmidt
Quoted 6 lines · Benjamin Herrenschmidt
arch/powerpc/kernel/setup_64.c +0 -0
@@ -10,7 +10,7 @@
  *      2 of the License, or (at your option) any later version.
  */
Quoted 5 lines

arch/powerpc/kernel/setup_64.c line 13

Quoted 2 lines
arch/powerpc/kernel/setup_64.c +1 -1
-#undef DEBUG
+#define DEBUG

Ooops... sent the wrong version. Will send an updated one later, if there are no other comments.

Looks like you merged the version with #define DEBUG.

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/kernel/setup_64.c#n13

cheers