[PATCH 1/3] ARM: CSR: Adding CSR SiRFprimaII board support

[Russell King - ARM Linux]

On Wed, Jul 06, 2011 at 02:47:56AM -0700, Barry Song wrote:
> diff --git a/arch/arm/mach-prima2/include/mach/io.h b/arch/arm/mach-prima2/include/mach/io.h
> new file mode 100644
> index 0000000..fc54f16
> --- /dev/null
> +++ b/arch/arm/mach-prima2/include/mach/io.h
> @@ -0,0 +1,21 @@
> +/*
> + * arch/arm/mach-prima2/include/mach/io.h
> + *
> + * Copyright (c) 2011 Cambridge Silicon Radio Limited, a CSR plc group company.
> + *
> + * Licensed under GPLv2 or later.
> + */
> +
> +#ifndef __MACH_PRIMA2_IO_H
> +#define __MACH_PRIMA2_IO_H
> +
> +#define IO_SPACE_LIMIT 0xffffffff

Can folk please start putting comments in their io.h file explaining their
choice for this definition?  Looking through the existing files, it is
almost impossible to infer the reason the value was picked, which makes
future maintanence a headache.

IO_SPACE_LIMIT sets the upper bound for the PCI/ISA style IO accessor
macros (inb, et.al.)

My guidance is:

1. If you have no support for ISA/PCI/PC card drivers, then set this to
   zero to prevent ISA/PCI drivers reserving IO port space.  You should
   be able to leave __io() set to __typesafe_io() without risking any
   ISA driver stamping on memory as those drivers should no longer
   successfully initialize with this set to zero.

2. If you have MMIO-mapped IO space (eg, a PCI bridge which forwards
   MMIO accesses in a window to PCI IO space) or equivalent, then set
   this to the size of the window, or 64K-1.  Explain this.

3. If you have MMIO-mapped IO space which is scattered (eg, multiple
   PC cards with their IO space individually mapped as separate 64K
   blocks) then explain this and set it to 0xffffffff for the time
   being.

In any case, having the chosen value documented, and if it is for
specific devices on the board, documenting that too, would really
help.

I shall be making this change to asm/io.h shortly:

 #include <mach/io.h>

+/*
+ * This is the limit of PCI/ISA/PC card IO space, which is by default
+ * 64K if we have PC card, PCI or ISA support.  Otherwise, default to
+ * zero to prevent ISA/PCI drivers claiming IO space (and potentially
+ * oopsing.)
+ *
+ * Only set this larger if you really need inb() et.al. to operate over
+ * a larger address space (eg, for multiple MMIO-mapped PC card sockets
+ * as found on SA11x0 and PXA.)
+ */
+#ifndef IO_SPACE_LIMIT
+#if defined(CONFIG_PCI) || defined(CONFIG_ISA) || defined(CONFIG_PCCARD)
+#define IO_SPACE_LIMIT ((resource_size_t)0xffff)
+#else
+#define IO_SPACE_LIMIT ((resource_size_t)0)
+#endif
+#endif

Thanks.