floppy.c - workaround for FDC initialization error

From: Hans-Juergen Tappe
Date: Fri Jul 16 2004 - 09:42:19 EST


I worked on a problem with linux-2.6.7 and linux-2.4.25 not detecting the floppy controller:
When compiled into the kernel, the kernel said: "no floppy controllers found", even though linux had been loaded from floppy via BIOS access. When loaded as a module, everything worked fine.
This sounded very much like the bug at
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=57253 ,
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=60887 and
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=75687 , but this problem occurs again on the new hardware.

It seems that the interrupt mask had not been set, so the answering interrupt never reaches the system and the driver initialization times out.

The controller is part of a Winbond W83627HF SuperIO, connected via LPC and Intel ICH4 to a Pentium mobile Processor system.

The workaround was to insert a udelay() for the controller to settle from it's first reset, if compiled as a module and only on the initializing reset, if the version is still FDC_NONE.

For other tests, I moved around the code in the process of linking and with my own entry point within main.c. I wanted to figure out, whether any dependency on other modules or processes before init() would become visible. This did not help, as did inserting waiting code as found in fdc_dtr, where similar circumstances have been documented.

Some questions to this mailing list:
- Does anyone have an idea of what the winbond controller is waiting
- Is this an appropriate workaround or patch?
- Is this the right place to wait or should I wait within floppy_init()
somewhere before user_reset_fdc(-1,FD_RESET_ALWAYS,0)?
- Is this the right way of waiting 2200 usec?
- Are there any other experiences with the Winbond W83627HF SuperIO
regarding floppy functionality?

Hans-Jürgen Tappe

--- linux/drivers/block/floppy.c_orig 2004-06-16 07:18:59 +0200
+++ linux/drivers/block/floppy.c 2004-07-16 15:51:53 +0200
@@ -4458,6 +4458,12 @@
if (FDCS->address != -1) {
fd_outb(FDCS->dor, FD_DOR);
+#ifndef MODULE
+ /* only before initialization */
+ if (FDCS->version == FDC_NONE)
+ /* Wait for the FDC to be ready */
+ udelay(2200);
fdc = 0;

Hans-Jürgen Tappe
Am Pfaffenstein 14
55270 Klein-Winternheim
Phone: +49-61 36-99 48-0
Fax: +49-61 36-99 48-10

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