drivers/misc: Add ASpeed LPC control driver

In order to manage server systems, there is typically another processor known as a BMC (Baseboard Management Controller) which is responsible for powering the server and other various elements, sometimes fans, often the system flash.

The Aspeed BMC family which is what is used on OpenPOWER machines and a number of x86 as well is typically connected to the host via an LPC (Low Pin Count) bus (among others).

The LPC bus is an ISA bus on steroids. It's generally used by the BMC chip to provide the host with access to the system flash (via MEM/FW cycles) that contains the BIOS or other host firmware along with a number of SuperIO-style IOs (via IO space) such as UARTs, IPMI controllers.

On the BMC chip side, this is all configured via a bunch of registers whose content is related to a given policy of what devices are exposed at a per system level, which is system/vendor specific, so we don't want to bolt that into the BMC kernel. This started with a need to provide something nicer than /dev/mem for user space to configure these things.

One important aspect of the configuration is how the MEM/FW space is exposed to the host (ie, the x86 or POWER). Some registers in that bridge can define a window remapping all or portion of the LPC MEM/FW space to a portion of the BMC internal bus, with no specific limits imposed in HW.

I think it makes sense to ensure that this window is configured by a kernel driver that can apply some serious sanity checks on what it is configured to map.

In practice, user space wants to control this by flipping the mapping between essentially two types of portions of the BMC address space:

- The flash space. This is a region of the BMC MMIO space that
more/less directly maps the system flash (at least for reads, writes are somewhat more complicated).

- One (or more) reserved area(s) of the BMC physical memory.

The latter is needed for a number of things, such as avoiding letting the host manipulate the innards of the BMC flash controller via some evil backdoor, we want to do flash updates by routing the window to a portion of memory (under control of a mailbox protocol via some separate set of registers) which the host can use to write new data in bulk and then request the BMC to flash it. There are other uses, such as allowing the host to boot from an in-memory flash image rather than the one in flash (very handy for continuous integration and test, the BMC can just download new images).

It is important to note that due to the way the ASpeed chip lets the kernel configure the mapping between host LPC addresses and BMC ram addresses the offset within the window must be a multiple of size. Not doing so will fragment the accessible space rather than simply moving 'zero' upwards. This is caused by the nature of HICR8 being a mask and the way host LPC addresses are translated.

---
v2:
Removed unused functions
Removed use of access_ok()
All input is evil
Reworked the interface as per Benjamin Herrenschmidts vision
V3:
Removed 'default y' from Kconfig
Reordered ioctl() struct fields
Reworeded some comments

 drivers/misc/Kconfig                 |   8 ++
 drivers/misc/Makefile                |   1 +
 drivers/misc/aspeed-lpc-ctrl.c       | 264 +++++++++++++++++++++++++++++++++++
 include/uapi/linux/aspeed-lpc-ctrl.h |  35 +++++
 4 files changed, 308 insertions(+)
 create mode 100644 drivers/misc/aspeed-lpc-ctrl.c
 create mode 100644 include/uapi/linux/aspeed-lpc-ctrl.h

index 64971baf11fa..4758c8f27952 100644
@@ -766,6 +766,14 @@ config PANEL_BOOT_MESSAGE
 	  An empty message will only clear the display at driver init time. Any other
 	  printf()-formatted message is valid with newline and escape codes.
 
+config ASPEED_LPC_CTRL
+	depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP && MFD_SYSCON
+	bool "Build a driver to control the BMC to HOST LPC bus"
+	---help---
+	  Provides a driver to control the HOST LPC to BMC mappings
+	  through ioctl()s, the driver aso provides a read/write interface to a
+	  BMC ram region where host LPC read/write region can be buffered.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"

index 31983366090a..de1925a9c80b 100644
@@ -53,6 +53,7 @@ obj-$(CONFIG_ECHO)		+= echo/
 obj-$(CONFIG_VEXPRESS_SYSCFG)	+= vexpress-syscfg.o
 obj-$(CONFIG_CXL_BASE)		+= cxl/
 obj-$(CONFIG_PANEL)             += panel.o
+obj-$(CONFIG_ASPEED_LPC_CTRL)	+= aspeed-lpc-ctrl.o
 
 lkdtm-$(CONFIG_LKDTM)		+= lkdtm_core.o
 lkdtm-$(CONFIG_LKDTM)		+= lkdtm_bugs.o

new file mode 100644
index 000000000000..de4d3a9d04d3
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2017 IBM Corp.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#ifndef _UAPI_LINUX_ASPEED_LPC_CTRL_H
+#define _UAPI_LINUX_ASPEED_LPC_CTRL_H
+
+#include <linux/ioctl.h>
+
+/* Window types */
+#define ASPEED_LPC_CTRL_WINDOW_FLASH	1
+#define ASPEED_LPC_CTRL_WINDOW_MEMORY	2
+
+struct aspeed_lpc_ctrl_mapping {
+	__u32	addr;
+	__u32	offset;
+	__u32	size;
+	__u8	window_type;
+	__u8	window_id;
+};
+
+#define __ASPEED_LPC_CTRL_IOCTL_MAGIC	0xb2
+
+#define ASPEED_LPC_CTRL_IOCTL_GET_SIZE	_IOWR(__ASPEED_LPC_CTRL_IOCTL_MAGIC, \
+		0x00, struct aspeed_lpc_ctrl_mapping)
+
+#define ASPEED_LPC_CTRL_IOCTL_MAP	_IOW(__ASPEED_LPC_CTRL_IOCTL_MAGIC, \
+		0x01, struct aspeed_lpc_ctrl_mapping)
+
+#endif /* _UAPI_LINUX_ASPEED_LPC_CTRL_H */

2.11.0

I'd like to get some acks or reviewed-by from some PPC people on this before accepting it, to let me know that they are ok with this driver as-is.

thanks,

greg k-h