[PATCH] powerpc: serial port discovery (#2)

This moves the discovery of legacy serial ports to a separate file,
makes it common to ppc32 and ppc64, and reworks it to use the new OF
address translators to get to the ports early. This new version can also
detect some PCI serial cards using legacy chips and will probably match
those discovered port with the default console choice.

Only ppc64 gets udbg still yet, unifying udbg isn't finished yet.

It also adds some speed-probing code to udbg so that the default console
can come up at the same speed it was set to by the firmware.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 53 insertions, 10 deletions

diff --git a/arch/powerpc/kernel/udbg_16550.c b/arch/powerpc/kernel/udbg_16550.c
index 9313574ab935..50fd376446c9 100644
--- a/arch/powerpc/kernel/udbg_16550.c
+++ b/arch/powerpc/kernel/udbg_16550.c
@@ -43,6 +43,8 @@ struct NS16550 {
 #define LSR_TEMT 0x40  /* Xmitter empty */
 #define LSR_ERR  0x80  /* Error */
 
+#define LCR_DLAB 0x80
+
 static volatile struct NS16550 __iomem *udbg_comport;
 
 static void udbg_550_putc(unsigned char c)
@@ -77,29 +79,70 @@ static unsigned char udbg_550_getc(void)
         return 0;
 }
 
-void udbg_init_uart(void __iomem *comport, unsigned int speed)
+void udbg_init_uart(void __iomem *comport, unsigned int speed,
+                    unsigned int clock)
 {
-        u16 dll = speed ? (115200 / speed) : 12;
+        unsigned int dll, base_bauds = clock / 16;
+
+        if (speed == 0)
+                speed = 9600;
+        dll = base_bauds / speed;
 
         if (comport) {
                 udbg_comport = (struct NS16550 __iomem *)comport;
                 out_8(&udbg_comport->lcr, 0x00);
                 out_8(&udbg_comport->ier, 0xff);
                 out_8(&udbg_comport->ier, 0x00);
-                out_8(&udbg_comport->lcr, 0x80);        /* Access baud rate */
-                out_8(&udbg_comport->dll, dll & 0xff);  /* 1 = 115200,  2 = 57600,
-                                                           3 = 38400, 12 = 9600 baud */
-                out_8(&udbg_comport->dlm, dll >> 8);    /* dll >> 8 which should be zero
-                                                           for fast rates; */
-                out_8(&udbg_comport->lcr, 0x03);        /* 8 data, 1 stop, no parity */
-                out_8(&udbg_comport->mcr, 0x03);        /* RTS/DTR */
-                out_8(&udbg_comport->fcr ,0x07);        /* Clear & enable FIFOs */
+                out_8(&udbg_comport->lcr, LCR_DLAB);
+                out_8(&udbg_comport->dll, dll & 0xff);
+                out_8(&udbg_comport->dlm, dll >> 8);
+                /* 8 data, 1 stop, no parity */
+                out_8(&udbg_comport->lcr, 0x03);
+                /* RTS/DTR */
+                out_8(&udbg_comport->mcr, 0x03);
+                /* Clear & enable FIFOs */
+                out_8(&udbg_comport->fcr ,0x07);
                 udbg_putc = udbg_550_putc;
                 udbg_getc = udbg_550_getc;
                 udbg_getc_poll = udbg_550_getc_poll;
         }
 }
 
+unsigned int udbg_probe_uart_speed(void __iomem *comport, unsigned int clock)
+{
+        unsigned int dll, dlm, divisor, prescaler, speed;
+        u8 old_lcr;
+        volatile struct NS16550 __iomem *port = comport;
+
+        old_lcr = in_8(&port->lcr);
+
+        /* select divisor latch registers.  */
+        out_8(&port->lcr, LCR_DLAB);
+
+        /* now, read the divisor */
+        dll = in_8(&port->dll);
+        dlm = in_8(&port->dlm);
+        divisor = dlm << 8 | dll;
+
+        /* check prescaling */
+        if (in_8(&port->mcr) & 0x80)
+                prescaler = 4;
+        else
+                prescaler = 1;
+
+        /* restore the LCR */
+        out_8(&port->lcr, old_lcr);
+
+        /* calculate speed */
+        speed = (clock / prescaler) / (divisor * 16);
+
+        /* sanity check */
+        if (speed < 9600 || speed > 115200)
+                speed = 9600;
+
+        return speed;
+}
+
 #ifdef CONFIG_PPC_MAPLE
 void udbg_maple_real_putc(unsigned char c)
 {