patch-2.1.106 linux/arch/m68k/mm/hwtest.c

• Lines: 82
• Date: Sat Jun 13 13:14:33 1998
• Orig file: v2.1.105/linux/arch/m68k/mm/hwtest.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.1.105/linux/arch/m68k/mm/hwtest.c linux/arch/m68k/mm/hwtest.c
@@ -0,0 +1,81 @@
+/* Tests for presence or absence of hardware registers.
+ * This code was originally in atari/config.c, but I noticed
+ * that it was also in drivers/nubus/nubus.c and I wanted to
+ * use it in hp300/config.c, so it seemed sensible to pull it
+ * out into its own file.
+ * 
+ * The test is for use when trying to read a hardware register
+ * that isn't present would cause a bus error. We set up a 
+ * temporary handler so that this doesn't kill the kernel.
+ *
+ * There is a test-by-reading and a test-by-writing; I present
+ * them here complete with the comments from the original atari
+ * config.c...
+ *                -- PMM <pmaydell@chiark.greenend.org.uk>, 05/1998
+ */
+
+/* This function tests for the presence of an address, specially a
+ * hardware register address. It is called very early in the kernel
+ * initialization process, when the VBR register isn't set up yet. On
+ * an Atari, it still points to address 0, which is unmapped. So a bus
+ * error would cause another bus error while fetching the exception
+ * vector, and the CPU would do nothing at all. So we needed to set up
+ * a temporary VBR and a vector table for the duration of the test.
+ */
+
+int hwreg_present( volatile void *regp )
+{
+    int	ret = 0;
+    long	save_sp, save_vbr;
+    long	tmp_vectors[3];
+
+    __asm__ __volatile__
+	(	"movec	%/vbr,%2\n\t"
+		"movel	#Lberr1,%4@(8)\n\t"
+                "movec	%4,%/vbr\n\t"
+		"movel	%/sp,%1\n\t"
+		"moveq	#0,%0\n\t"
+		"tstb	%3@\n\t"  
+		"nop\n\t"
+		"moveq	#1,%0\n"
+                "Lberr1:\n\t"
+		"movel	%1,%/sp\n\t"
+		"movec	%2,%/vbr"
+		: "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
+		: "a" (regp), "a" (tmp_vectors)
+                );
+
+    return( ret );
+}
+  
+/* Basically the same, but writes a value into a word register, protected
+ * by a bus error handler. Returns 1 if successful, 0 otherwise.
+ */
+
+int hwreg_write( volatile void *regp, unsigned short val )
+{
+	int		ret;
+	long	save_sp, save_vbr;
+	long	tmp_vectors[3];
+
+	__asm__ __volatile__
+	(	"movec	%/vbr,%2\n\t"
+		"movel	#Lberr2,%4@(8)\n\t"
+		"movec	%4,%/vbr\n\t"
+		"movel	%/sp,%1\n\t"
+		"moveq	#0,%0\n\t"
+		"movew	%5,%3@\n\t"  
+		"nop	\n\t"	/* If this nop isn't present, 'ret' may already be
+				 * loaded with 1 at the time the bus error
+				 * happens! */
+		"moveq	#1,%0\n"
+	"Lberr2:\n\t"
+		"movel	%1,%/sp\n\t"
+		"movec	%2,%/vbr"
+		: "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
+		: "a" (regp), "a" (tmp_vectors), "g" (val)
+	);
+
+	return( ret );
+}
+