powerpc/xmon: Paged output for paca display

The paca display is already more than 24 lines, which can be problematic
if you have an old school 80x24 terminal, or more likely you are on a
virtual terminal which does not scroll for whatever reason.

This patch adds a new command "#", which takes a single (hex) numeric
argument: lines per page. It will cause the output of "dp" and "dpa"
to be broken into pages, if necessary.

Sample output:

0:mon> # 10
0:mon> dp1
paca for cpu 0x1 @ c00000000fdc0480:
 possible         = yes
 present          = yes
 online           = yes
 lock_token       = 0x8000            	(0x8)
 paca_index       = 0x1               	(0xa)
 kernel_toc       = 0xc000000000eb2400	(0x10)
 kernelbase       = 0xc000000000000000	(0x18)
 kernel_msr       = 0xb000000000001032	(0x20)
 emergency_sp     = 0xc00000003ffe8000	(0x28)
 mc_emergency_sp  = 0xc00000003ffe4000	(0x2e0)
 in_mce           = 0x0               	(0x2e8)
 data_offset      = 0x7f170000        	(0x30)
 hw_cpu_id        = 0x8               	(0x38)
 cpu_start        = 0x1               	(0x3a)
 kexec_state      = 0x0               	(0x3b)
[Hit a key (a:all, q:truncate, any:next page)]
0:mon>
 __current        = 0xc00000007e696620	(0x290)
 kstack           = 0xc00000007e6ebe30	(0x298)
 stab_rr          = 0xb               	(0x2a0)
 saved_r1         = 0xc00000007ef37860	(0x2a8)
 trap_save        = 0x0               	(0x2b8)
 soft_enabled     = 0x0               	(0x2ba)
 irq_happened     = 0x1               	(0x2bb)
 io_sync          = 0x0               	(0x2bc)
 irq_work_pending = 0x0               	(0x2bd)
 nap_state_lost   = 0x0               	(0x2be)
0:mon>

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
[mpe: Use bool, make some variables static]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/xmon/nonstdio.c

@@ -11,10 +11,25 @@
 #include <asm/time.h>
 #include "nonstdio.h"
 
+static bool paginating, paginate_skipping;
+static unsigned long paginate_lpp; /* Lines Per Page */
+static unsigned long paginate_pos;
 
-static int xmon_write(const void *ptr, int nb)
+void xmon_start_pagination(void)
 {
-	return udbg_write(ptr, nb);
+	paginating = true;
+	paginate_skipping = false;
+	paginate_pos = 0;
+}
+
+void xmon_end_pagination(void)
+{
+	paginating = false;
+}
+
+void xmon_set_pagination_lpp(unsigned long lpp)
+{
+	paginate_lpp = lpp;
 }
 
 static int xmon_readchar(void)
@@ -24,6 +39,51 @@ static int xmon_readchar(void)
 	return -1;
 }
 
+static int xmon_write(const char *ptr, int nb)
+{
+	int rv = 0;
+	const char *p = ptr, *q;
+	const char msg[] = "[Hit a key (a:all, q:truncate, any:next page)]";
+
+	if (nb <= 0)
+		return rv;
+
+	if (paginating && paginate_skipping)
+		return nb;
+
+	if (paginate_lpp) {
+		while (paginating && (q = strchr(p, '\n'))) {
+			rv += udbg_write(p, q - p + 1);
+			p = q + 1;
+			paginate_pos++;
+
+			if (paginate_pos >= paginate_lpp) {
+				udbg_write(msg, strlen(msg));
+
+				switch (xmon_readchar()) {
+				case 'a':
+					paginating = false;
+					break;
+				case 'q':
+					paginate_skipping = true;
+					break;
+				default:
+					/* nothing */
+					break;
+				}
+
+				paginate_pos = 0;
+				udbg_write("\r\n", 2);
+
+				if (paginate_skipping)
+					return nb;
+			}
+		}
+	}
+
+	return rv + udbg_write(p, nb - (p - ptr));
+}
+
 int xmon_putchar(int c)
 {
 	char ch = c;