b43: Add PIO support for PCMCIA devices

This adds PIO support back (D'oh!) for PCMCIA devices.
This is a complete rewrite of the old PIO code. It does actually work
and we get reasonable performance out of it on a modern machine.
On a PowerBook G4 I get a few MBit for TX and a few more for RX.
So it doesn't work as well as DMA (of course), but it's a _lot_ faster
than the old PIO code (only got a few kBit with that).

The limiting factor is the host CPU speed. So it will generate 100%
CPU usage when the network interface is heavily loaded. A voluntary preemption
point in the RX path makes sure Desktop Latency isn't hurt.

PIO is needed for 16bit PCMCIA devices, as we really don't want to poke with
the braindead DMA mechanisms on PCMCIA sockets. Additionally, not all
PCMCIA sockets do actually support DMA in 16bit mode (mine doesn't).

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/net/wireless/b43/Kconfig b/drivers/net/wireless/b43/Kconfig
index 8bc4bc4..94f0455 100644
--- a/drivers/net/wireless/b43/Kconfig
+++ b/drivers/net/wireless/b43/Kconfig
@@ -62,6 +62,13 @@ config B43_PCMCIA
 
 	  If unsure, say N.
 
+# Data transfers to the device via PIO
+# This is only needed on PCMCIA devices. All others can do DMA properly.
+config B43_PIO
+	bool
+	depends on B43 && (B43_PCMCIA || B43_FORCE_PIO)
+	default y
+
 config B43_NPHY
 	bool "Pre IEEE 802.11n support (BROKEN)"
 	depends on B43 && EXPERIMENTAL && BROKEN
@@ -94,3 +101,13 @@ config B43_DEBUG
 
 	  Say Y, if you want to find out why the driver does not
 	  work for you.
+
+config B43_FORCE_PIO
+	bool "Force usage of PIO instead of DMA"
+	depends on B43 && B43_DEBUG
+	---help---
+	  This will disable DMA and always enable PIO instead.
+
+	  Say N!
+	  This is only for debugging the PIO engine code. You do
+	  _NOT_ want to enable this.