Re: [PATCH] drivers/char/serial.c bug in ST16C654 detection

From: Val Henson (val@nmt.edu)
Date: Wed May 16 2001 - 17:12:45 EST

Anyone know where Ted Tso is? He hasn't posted in several weeks.
Alan, will you put this in -ac? This patch fixes a bug in serial.c
that causes a crash on machines with a ST16C654.

On Tue, May 15, 2001 at 09:52:01AM -0400, Stuart MacDonald wrote:

> Kernel version? Distribution? Are you using a serial console?

2.4.5-pre1 (see patch).

> The revision should always be saved if it's available. Hmm.
> I didn't look carefully yesterday. The DLL always contains the
> revision for the 85x family. Why do you think it doesn't?

Because the comment was ambiguous. I don't have the data sheet for
the 85x family so I just wrote the code according to the comment.
I'll change the comment to make it clear.

> I think your patch below is good, I'm just mystified by this
> kablooey thing.

Thanks. Corrected version of the patch is below.

-VAL

--- linux-2.4.5-pre1/drivers/char/serial.c Thu Apr 19 00:26:34 2001
+++ linux/drivers/char/serial.c Thu May 17 03:12:09 2001
@@ -3507,7 +3507,7 @@
                                       struct serial_state *state,
                                       unsigned long flags)
 {
- unsigned char scratch, scratch2, scratch3;
+ unsigned char scratch, scratch2, scratch3, scratch4;
 
         /*
          * First we check to see if it's an Oxford Semiconductor UART.
@@ -3548,20 +3548,33 @@
          * then reading back DLL and DLM. If DLM reads back 0x10,
          * then the UART is a XR16C850 and the DLL contains the chip
          * revision. If DLM reads back 0x14, then the UART is a
- * XR16C854.
- *
+ * XR16C854 and the DLL contains the chip revision.
          */
+
+ /* Save the DLL and DLM */
+
         serial_outp(info, UART_LCR, UART_LCR_DLAB);
+ scratch3 = serial_inp(info, UART_DLL);
+ scratch4 = serial_inp(info, UART_DLM);
+
         serial_outp(info, UART_DLL, 0);
         serial_outp(info, UART_DLM, 0);
- state->revision = serial_inp(info, UART_DLL);
+ scratch2 = serial_inp(info, UART_DLL);
         scratch = serial_inp(info, UART_DLM);
         serial_outp(info, UART_LCR, 0);
+
         if (scratch == 0x10 || scratch == 0x14) {
+ state->revision = scratch2;
                 state->type = PORT_16850;
                 return;
         }
 
+ /* Restore the DLL and DLM */
+
+ serial_outp(info, UART_LCR, UART_LCR_DLAB);
+ serial_outp(info, UART_DLL, scratch3);
+ serial_outp(info, UART_DLM, scratch4);
+ serial_outp(info, UART_LCR, 0);
         /*
          * We distinguish between the '654 and the '650 by counting
          * how many bytes are in the FIFO. I'm using this for now,

-
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This archive was generated by hypermail 2b29 : Wed May 23 2001 - 21:00:20 EST