Re: [PATCH v6] drivers/misc: Add Aspeed LPC control driver

[Suraj Jitindar Singh]

On Thu, 2017-03-02 at 12:01 +1100, Cyril Bur wrote:
> On Wed, 2017-02-22 at 16:11 +1100, Suraj Jitindar Singh wrote:
> > 
> > On Fri, 2017-02-17 at 14:28 +1100, Cyril Bur wrote:
> > 
> > I may be too late, but see below...
> > > 
> > > 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:
> > > 
> > > ÂÂÂ- 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).
> > > 
> > > ÂÂÂ- 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.
> > > 
> > > Signed-off-by: Cyril Bur <cyrilbur@xxxxxxxxx>
> > > ---
> > > v2:
> > > ÂÂÂRemoved unused functions
> > > ÂÂÂRemoved use of access_ok()
> > > ÂÂÂAll input is evil
> > > ÂÂÂReworked the interface as per Benjamin Herrenschmidts vision
> > > v3:
> > > ÂÂÂRemoved 'default y' from Kconfig
> > > ÂÂÂReordered ioctl() struct fields
> > > ÂÂÂReworeded some comments
> > > v4:
> > > ÂÂÂReorder ioctl() struct fields (again)
> > > v5:
> > > ÂÂÂStyle cleanups
> > > ÂÂÂUse of_address_to_resource()
> > > ÂÂÂDocument ioctl structure fields
> > > v6:
> > > ÂÂÂCheck and fail ioctl() if flags field non-zero
> > > 
> > > Âdrivers/misc/KconfigÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ|ÂÂÂ8 ++
> > > Âdrivers/misc/MakefileÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ|ÂÂÂ1 +
> > > Âdrivers/misc/aspeed-lpc-ctrl.cÂÂÂÂÂÂÂ| 267
> > > +++++++++++++++++++++++++++++++++++
> > > Âinclude/uapi/linux/aspeed-lpc-ctrl.h |ÂÂ60 ++++++++
> > > Â4 files changed, 336 insertions(+)
> > > Âcreate mode 100644 drivers/misc/aspeed-lpc-ctrl.c
> > > Âcreate mode 100644 include/uapi/linux/aspeed-lpc-ctrl.h
> > > 
> > > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> > > index 64971baf11fa..7dc4c369012f 100644
> > > --- a/drivers/misc/Kconfig
> > > +++ b/drivers/misc/Kconfig
> > > @@ -766,6 +766,14 @@ config PANEL_BOOT_MESSAGE
> > > Â	ÂÂAn empty message will only clear the display at driver
> > > init time. Any other
> > > Â	ÂÂprintf()-formatted message is valid with newline and
> > > escape codes.
> > > Â
> > > +config ASPEED_LPC_CTRL
> > > +	depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP &&
> > > MFD_SYSCON
> > > +	tristate "Aspeed ast2400/2500 HOST LPC to BMC bridge
> > > control"
> > > +	---help---
> > > +	ÂÂControl Aspeed ast2400/2500 HOST LPC to BMC mappings
> > > through
> > > +	ÂÂioctl()s, the driver also provides a read/write
> > > interface
> > > to a BMC ram
> > > +	ÂÂregion where the host LPC read/write region can be
> > > buffered.
> > > +
> > > Âsource "drivers/misc/c2port/Kconfig"
> > > Âsource "drivers/misc/eeprom/Kconfig"
> > > Âsource "drivers/misc/cb710/Kconfig"
> > > diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> > > index 31983366090a..de1925a9c80b 100644
> > > --- a/drivers/misc/Makefile
> > > +++ b/drivers/misc/Makefile
> > > @@ -53,6 +53,7 @@ obj-$(CONFIG_ECHO)		+= echo/
> > > Âobj-$(CONFIG_VEXPRESS_SYSCFG)	+= vexpress-syscfg.o
> > > Âobj-$(CONFIG_CXL_BASE)		+= cxl/
> > > Âobj-$(CONFIG_PANEL)ÂÂÂÂÂÂÂÂÂÂÂÂÂ+= panel.o
> > > +obj-$(CONFIG_ASPEED_LPC_CTRL)	+= aspeed-lpc-ctrl.o
> > > Â
> > > Âlkdtm-$(CONFIG_LKDTM)		+= lkdtm_core.o
> > > Âlkdtm-$(CONFIG_LKDTM)		+= lkdtm_bugs.o
> > > diff --git a/drivers/misc/aspeed-lpc-ctrl.c
> > > b/drivers/misc/aspeed-
> > > lpc-ctrl.c
> > > new file mode 100644
> > > index 000000000000..f6acbe1d9378
> > > --- /dev/null
> > > +++ b/drivers/misc/aspeed-lpc-ctrl.c
> > > @@ -0,0 +1,267 @@
> > > +/*
> > > + * Copyright 2017 IBM Corporation
> > > + *
> > > + * 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.
> > > + */
> > > +
> > > +#include <linux/mfd/syscon.h>
> > > +#include <linux/miscdevice.h>
> > > +#include <linux/mm.h>
> > > +#include <linux/module.h>
> > > +#include <linux/of_address.h>
> > > +#include <linux/platform_device.h>
> > > +#include <linux/poll.h>
> > > +#include <linux/regmap.h>
> > > +
> > > +#include <linux/aspeed-lpc-ctrl.h>
> > > +
> > > +#define DEVICE_NAME	"aspeed-lpc-ctrl"
> > > +
> > > +#define HICR7 0x8
> > > +#define HICR8 0xc
> > > +
> > > +struct aspeed_lpc_ctrl {
> > > +	struct miscdevice	miscdev;
> > > +	struct regmap		*regmap;
> > > +	phys_addr_t		mem_base;
> > > +	resource_size_t		mem_size;
> > > +	u32		pnor_size;
> > > +	u32		pnor_base;
> > > +};
> > > +
> > > +static struct aspeed_lpc_ctrl *file_aspeed_lpc_ctrl(struct file
> > > *file)
> > > +{
> > > +	return container_of(file->private_data, struct
> > > aspeed_lpc_ctrl,
> > > +			miscdev);
> > > +}
> > > +
> > > +static int aspeed_lpc_ctrl_mmap(struct file *file, struct
> > > vm_area_struct *vma)
> > > +{
> > > +	struct aspeed_lpc_ctrl *lpc_ctrl =
> > > file_aspeed_lpc_ctrl(file);
> > > +	unsigned long vsize = vma->vm_end - vma->vm_start;
> > > +	pgprot_t prot = vma->vm_page_prot;
> > > +
> > > +	if (vma->vm_pgoff + vsize > lpc_ctrl->mem_base +
> > > lpc_ctrl-
> > > > 
> > > > mem_size)
> > > +		return -EINVAL;
> > > +
> > > +	/* ast2400/2500 AHB accesses are not cache coherent */
> > > +	prot = pgprot_dmacoherent(prot);
> > > +
> > > +	if (remap_pfn_range(vma, vma->vm_start,
> > > +		(lpc_ctrl->mem_base >> PAGE_SHIFT) + vma-
> > > >vm_pgoff,
> > > +		vsize, prot))
> > > +		return -EAGAIN;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static long aspeed_lpc_ctrl_ioctl(struct file *file, unsigned
> > > int
> > > cmd,
> > > +		unsigned long param)
> > > +{
> > > +	struct aspeed_lpc_ctrl *lpc_ctrl =
> > > file_aspeed_lpc_ctrl(file);
> > > +	void __user *p = (void __user *)param;
> > > +	struct aspeed_lpc_ctrl_mapping map;
> > > +	u32 addr;
> > > +	u32 size;
> > > +	long rc;
> > > +
> > > +	if (copy_from_user(&map, p, sizeof(map)))
> > > +		return -EFAULT;
> > > +
> > > +	if (map.flags != 0)
> > > +		return -EINVAL;
> > > +
> > > +	switch (cmd) {
> > > +	case ASPEED_LPC_CTRL_IOCTL_GET_SIZE:
> > > +		/* The flash windows don't report their size */
> > > +		if (map.window_type !=
> > > ASPEED_LPC_CTRL_WINDOW_MEMORY)
> > > +			return -EINVAL;
> > > +
> > > +		/* Support more than one window id in the future
> > > */
> > > +		if (map.window_id != 0)
> > > +			return -EINVAL;
> > > +
> > > +		map.size = lpc_ctrl->mem_size;
> > > +
> > > +		return copy_to_user(p, &map, sizeof(map)) ?
> > > -EFAULT
> > > : 0;
> > > +	case ASPEED_LPC_CTRL_IOCTL_MAP:
> > > +
> > > +		/*
> > > +		Â* The top half of HICR7 is the MSB of the BMC
> > > address of the
> > > +		Â* mapping.
> Hi Suraj,
> 
> I'm all for writing this out as many times as possible to be sure
> everyone understands it. I think a visual diagram would be fantastic,
> I'd love to do one in my infinite spare time. It may be useful to
> link
> to Benhs comments in skiboot for another wording of how these two
> registers work skiboot/hw/ast-bmc/ast-io.c.
> 
> > 
> > How about: HICR7[31:16] is the [offset into BMC memory/most
> > significant
> > two bytes fo the BMC address] of the mapping.
> > > 
> > > +		Â* The bottom half of HICR7 is
> > > the MSB of the HOST LPC
> > HICR7[15:0] is the [offset on the HOST LPC firmware address
> > space/most
> > fisnificant two bytes of the HOST LPC firmware address space] of
> > the
> > mapping
> Yes, this appears correct.
> 
> > 
> > > 
> > > +		Â* firmware space address of the mapping.
> > > +		Â*
> > > +		Â* The 1 bits in the top of half of HICR8
> > > represent
> > > the bits
> > > +		Â* (in the requested address) that should be
> > > ignored
> > > and
> > > +		Â* replaced with those from the top half of
> > > HICR7.
> > HICR8[31:16] represents a mask of the bits which should be taken
> > from
> > HICR7[31:16] and placed in the BMC address.
> Yes.
> 
> > 
> > > 
> > > +		Â* The 1 bits in the bottom half of HICR8
> > > represent
> > > the bits
> > > +		Â* (in the requested address) that should be
> > > kept
> > > and pass
> > > +		Â* into the BMC address space.
> > HICR8[15:0] represents a mask of the bits which should be taken
> > from
> > LPC_ADDR[31:16] and placed in the BMC address.
> > 
> > If I understand correctly, we basically end up with:
> > 
> > BMC_ADDR[31:0] = (BMC_OFFSET + LPC_OFFSET + INDEX) << 16 + OFFSET
> > where:
> > BMC_OFFSET = HICR7[31:16] & HICR8[31:16] - The offset into bmc
> > memory
> > of where the window is.
> > LPC_OFFSET = LPC_ADDR[31:16] - HICR7[15:0] - The offset on the lpc
> > bus
> > of where we created the window.
> > INDEX = LPC_ADDR[31:16] & HICR8[15:0] - High bits of the lpc
> > address
> > which we use in the bmc address.
> > OFFSET = LPC_ADDR[15:0] - Low bits of the lpc address which we use
> > in
> > the bmc address.
> > > 
> > > +		Â*/
> This sounds right to me.
> 
> > 
> > > 
> > > +
> > > +		/*
> > > +		Â* It doesn't make sense to talk about a size or
> > > offset with
> > > +		Â* low 16 bits set. Both HICR7 and HICR8 talk
> > > about
> > > the top 16
> > > +		Â* bits of addresses and sizes.
> > > +		Â*/
> > > +
> > > +		if ((map.size & 0x0000ffff) || (map.offset &
> > > 0x0000ffff))
> > > +			return -EINVAL;
> > Am I missing something? Are you checking anywhere that map.size is
> > power-of-2 aligned?
> > > 
> > > +
> Not explicitly - I didn't want to be too restrictive. The conditions
> only protect against exploits. Any other values should *work* but
> produce interesting results. For example, it would be possible to map
> the same 64K BMC region to multiple 64K regions on the host - why one
> would do that I have no idea but you can.
> 
> > 
> > > 
> > > +		/*
> > > +		Â* Because of the way the masks work in HICR8
> > > offset
> > > has to
> > > +		Â* be a multiple of size.
> > > +		Â*/
> > > +		if (map.offset & (map.size - 1))
> > > +			return -EINVAL;
> > > +
> > > +		if (map.window_type ==
> > > ASPEED_LPC_CTRL_WINDOW_FLASH)
> > > {
> > > +			addr = lpc_ctrl->pnor_base;
> > > +			size = lpc_ctrl->pnor_size;
> > > +		} else if (map.window_type ==
> > > ASPEED_LPC_CTRL_WINDOW_MEMORY) {
> > > +			addr = lpc_ctrl->mem_base;
> > > +			size = lpc_ctrl->mem_size;
> > > +		} else {
> > > +			return -EINVAL;
> > > +		}
> > > +
> > > +		/* Check overflow first! */
> > > +		if (map.offset + map.size < map.offset ||
> > > +			map.offset + map.size > size)
> > > +			return -EINVAL;
> > > +
> > > +		if (map.size == 0 || map.size > size)
> > > +			return -EINVAL;
> > > +
> > > +		addr += map.offset;
> > > +
> > > +		/*
> > > +		Â* addr (host lpc address) is safe regardless of
> > > values. This
> > > +		Â* simply changes the address the host has to
> > > request on its
> > > +		Â* side of the LPC bus. This cannot impact the
> > > hosts
> > > own
> > > +		Â* memory space by surprise as LPC specific
> > > accessors are
> > > +		Â* required. The only strange thing that could
> > > be
> > > done is
> > > +		Â* setting the lower 16 bits but the shift takes
> > > care of that.
> > > +		Â*/
> > Don't you have to explicitly check that the bits 15:0 of map.addr
> > aren't set? Otherwise something could ask to map LPC address 0x1234
> > (map.addr = 0x1234), you will set HICR7[15:0] = 0 (map.addr >> 16).
> > So
> > when address 0x1234 is accessed on the lpc bus, this will map to
> > bmc
> > address 0x1234 instead of the expected 0x0 (since this is the base
> > lpc
> > address)?
> > 
> Yeah I didn't check, as you say the 0x1234 get thrown away by the
> shift. It appears I forgot to explicitly say that that the smallest
> valid value is 64K, I did say that about the size. I'd be surprised
> if
> a user didn't know this already but if you feel strongly about it I 
I don't feel that strongly... :)
> can
> resend with an error condition for it.
> 
> Thanks,
> 
> Cyril
> 
> > 
> > Or do we preclude the low 16 bits of map.addr from being set
> > somewhere
> > else?
> > > 
> > > +
> > > +		rc = regmap_write(lpc_ctrl->regmap, HICR7,
> > > +				(addr | (map.addr >> 16)));
> > > +		if (rc)
> > > +			return rc;
> > > +
> > > +		return regmap_write(lpc_ctrl->regmap, HICR8,
> > > +			(~(map.size - 1)) | ((map.size >> 16) -
> > > 1));
> > > +	}
> > > +
> > > +	return -EINVAL;
> > > +}
> > > +
> > > +static const struct file_operations aspeed_lpc_ctrl_fops = {
> > > +	.owner		= THIS_MODULE,
> > > +	.mmap		= aspeed_lpc_ctrl_mmap,
> > > +	.unlocked_ioctl	= aspeed_lpc_ctrl_ioctl,
> > > +};
> > > +
> > > +static int aspeed_lpc_ctrl_probe(struct platform_device *pdev)
> > > +{
> > > +	struct aspeed_lpc_ctrl *lpc_ctrl;
> > > +	struct device_node *node;
> > > +	struct resource resm;
> > > +	struct device *dev;
> > > +	int rc;
> > > +
> > > +	dev = &pdev->dev;
> > > +
> > > +	lpc_ctrl = devm_kzalloc(dev, sizeof(*lpc_ctrl),
> > > GFP_KERNEL);
> > > +	if (!lpc_ctrl)
> > > +		return -ENOMEM;
> > > +
> > > +	node = of_parse_phandle(dev->of_node, "flash", 0);
> > > +	if (!node) {
> > > +		dev_err(dev, "Didn't find host pnor flash
> > > node\n");
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	rc = of_address_to_resource(node, 1, &resm);
> > > +	of_node_put(node);
> > > +	if (rc) {
> > > +		dev_err(dev, "Couldn't address to resource for
> > > flash\n");
> > > +		return rc;
> > > +	}
> > > +
> > > +	lpc_ctrl->pnor_size = resource_size(&resm);
> > > +	lpc_ctrl->pnor_base = resm.start;
> > > +
> > > +	dev_set_drvdata(&pdev->dev, lpc_ctrl);
> > > +
> > > +	node = of_parse_phandle(dev->of_node, "memory-region",
> > > 0);
> > > +	if (!node) {
> > > +		dev_err(dev, "Didn't find reserved memory\n");
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	rc = of_address_to_resource(node, 0, &resm);
> > > +	of_node_put(node);
> > > +	if (rc) {
> > > +		dev_err(dev, "Couldn't address to resource for
> > > reserved memory\n");
> > > +		return -ENOMEM;
> > > +	}
> > > +
> > > +	lpc_ctrl->mem_size = resource_size(&resm);
> > > +	lpc_ctrl->mem_base = resm.start;
> > > +
> > > +	lpc_ctrl->regmap = syscon_node_to_regmap(
> > > +			pdev->dev.parent->of_node);
> > > +	if (IS_ERR(lpc_ctrl->regmap)) {
> > > +		dev_err(dev, "Couldn't get regmap\n");
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	lpc_ctrl->miscdev.minor = MISC_DYNAMIC_MINOR;
> > > +	lpc_ctrl->miscdev.name = DEVICE_NAME;
> > > +	lpc_ctrl->miscdev.fops = &aspeed_lpc_ctrl_fops;
> > > +	lpc_ctrl->miscdev.parent = dev;
> > > +	rc = misc_register(&lpc_ctrl->miscdev);
> > > +	if (rc)
> > > +		dev_err(dev, "Unable to register device\n");
> > > +	else
> > > +		dev_info(dev, "Loaded at 0x%08x (0x%08x)\n",
> > > +			lpc_ctrl->mem_base, lpc_ctrl->mem_size);
> > > +
> > > +	return rc;
> > > +}
> > > +
> > > +static int aspeed_lpc_ctrl_remove(struct platform_device *pdev)
> > > +{
> > > +	struct aspeed_lpc_ctrl *lpc_ctrl =
> > > dev_get_drvdata(&pdev-
> > > > 
> > > > dev);
> > > +
> > > +	misc_deregister(&lpc_ctrl->miscdev);
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static const struct of_device_id aspeed_lpc_ctrl_match[] = {
> > > +	{ .compatible = "aspeed,ast2400-lpc-ctrl" },
> > > +	{ .compatible = "aspeed,ast2500-lpc-ctrl" },
> > > +	{ },
> > > +};
> > > +
> > > +static struct platform_driver aspeed_lpc_ctrl_driver = {
> > > +	.driver = {
> > > +		.name		= DEVICE_NAME,
> > > +		.of_match_table = aspeed_lpc_ctrl_match,
> > > +	},
> > > +	.probe = aspeed_lpc_ctrl_probe,
> > > +	.remove = aspeed_lpc_ctrl_remove,
> > > +};
> > > +
> > > +module_platform_driver(aspeed_lpc_ctrl_driver);
> > > +
> > > +MODULE_DEVICE_TABLE(of, aspeed_lpc_ctrl_match);
> > > +MODULE_LICENSE("GPL");
> > > +MODULE_AUTHOR("Cyril Bur <cyrilbur@xxxxxxxxx>");
> > > +MODULE_DESCRIPTION("Control for aspeed 2400/2500 LPC HOST to BMC
> > > mappings");
> > > diff --git a/include/uapi/linux/aspeed-lpc-ctrl.h
> > > b/include/uapi/linux/aspeed-lpc-ctrl.h
> > > new file mode 100644
> > > index 000000000000..f96fa995a3f0
> > > --- /dev/null
> > > +++ b/include/uapi/linux/aspeed-lpc-ctrl.h
> > > @@ -0,0 +1,60 @@
> > > +/*
> > > + * 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
> > > +
> > > +/*
> > > + * This driver provides a window for the host to access a BMC
> > > resource
> > > + * across the BMC <-> Host LPC bus.
> > > + *
> > > + * window_type: The BMC resource that the host will access
> > > through
> > > the
> > > + * window. BMC flash and BMC RAM.
> > > + *
> > > + * window_id: For each window type there may be multiple
> > > windows,
> > > + * these are referenced by ID.
> > > + *
> > > + * flags: Reserved for future use, this field is expected to be
> > > + * zeroed.
> > > + *
> > > + * addr: Address on the host LPC bus that the specified window
> > > should
> > > + * be mapped. This address must be power of two aligned.
> > If I understand correctly -> AND a multiple of size?
> > > 
> > > + *
> > > + * offset: Offset into the BMC window that should be mapped to
> > > the
> > > + * host (at addr). This must be a multiple of size.
> > > + *
> > > + * size: The size of the mapping. The smallest possible size is
> > > 64K.
> > > + * This must be power of two aligned.
> > > + *
> > > + */
> > > +
> > > +struct aspeed_lpc_ctrl_mapping {
> > > +	__u8	window_type;
> > > +	__u8	window_id;
> > > +	__u16	flags;
> > > +	__u32	addr;
> > > +	__u32	offset;
> > > +	__u32	size;
> > > +};
> > > +
> > > +#define __ASPEED_LPC_CTRL_IOCTL_MAGIC	0xb2
> > > +
> > > +#define ASPEED_LPC_CTRL_IOCTL_GET_SIZE	_IOWR(__ASPEED_LPC
> > > _CTR
> > > L_IOCTL_MAGIC, \
> > > +		0x00, struct aspeed_lpc_ctrl_mapping)
> > > +
> > > +#define ASPEED_LPC_CTRL_IOCTL_MAP	_IOW(__ASPEED_LPC_CTRL_
> > > IOCT
> > > L_MAGIC, \
> > > +		0x01, struct aspeed_lpc_ctrl_mapping)
> > > +
> > > +#endif /* _UAPI_LINUX_ASPEED_LPC_CTRL_H */