Re: [PATCH v5 2/2] drivers/misc: Add Aspeed P2A control driver

[Andrew Jeffery]

Hi Patrick.

I've got some minor comments, otherwise it looks reasonable to me.

On Thu, 28 Feb 2019, at 12:22, Patrick Venture wrote:
> The ASPEED AST2400, and AST2500 in some configurations include a
> PCI-to-AHB MMIO bridge.  This bridge allows a server to read and write
> in the BMC's physical address space.  This feature is especially useful
> when using this bridge to send large files to the BMC.
> 
> The host may use this to send down a firmware image by staging data at a
> specific memory address, and in a coordinated effort with the BMC's
> software stack and kernel, transmit the bytes.
> 
> This driver enables the BMC to unlock the PCI bridge on demand, and
> configure it via ioctl to allow the host to write bytes to an agreed
> upon location.  In the primary use-case, the region to use is known
> apriori on the BMC, and the host requests this information.  Once this
> request is received, the BMC's software stack will enable the bridge and
> the region and then using some software flow control (possibly via IPMI
> packets), copy the bytes down.  Once the process is complete, the BMC
> will disable the bridge and unset any region involved.
> 
> The default behavior of this bridge when present is: enabled and all
> regions marked read-write.  This driver will fix the regions to be
> read-only and then disable the bridge entirely.
> 
> The memory regions protected are:
>  * BMC flash MMIO window
>  * System flash MMIO windows
>  * SOC IO (peripheral MMIO)
>  * DRAM
> 
> The DRAM region itself is all of DRAM and cannot be further specified.
> Once the PCI bridge is enabled, the host can read all of DRAM, and if
> the DRAM section is write-enabled, then it can write to all of it.
> 
> Signed-off-by: Patrick Venture <venture@xxxxxxxxxx>
> ---
> Changes for v5:
> - Fixup missing exit condition and remove extra jump.
> Changes for v4:
> - Added ioctl for reading back the memory-region configuration.
> - Cleaned up some unused variables.
> Changes for v3:
> - Deleted unused read and write methods.
> Changes for v2:
> - Dropped unused reads.
> - Moved call to disable bridge to before registering device.
> - Switch from using regs to using a syscon regmap. <<< IN PROGRESS
> - Updated the commit message. <<< TODO
> - Updated the bit flipped for SCU180_ENP2A
> - Dropped boolean region_specified variable.
> - Renamed p2a_ctrl in _probe to misc_ctrl per suggestion.
> - Renamed aspeed_p2a_region_search to aspeed_p2a_region_acquire
> - Updated commit message.
> ---
>  drivers/misc/Kconfig                 |   8 +
>  drivers/misc/Makefile                |   1 +
>  drivers/misc/aspeed-p2a-ctrl.c       | 456 +++++++++++++++++++++++++++
>  include/uapi/linux/aspeed-p2a-ctrl.h |  59 ++++
>  4 files changed, 524 insertions(+)
>  create mode 100644 drivers/misc/aspeed-p2a-ctrl.c
>  create mode 100644 include/uapi/linux/aspeed-p2a-ctrl.h
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index f417b06e11c5..9de1bafe5606 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -485,6 +485,14 @@ config VEXPRESS_SYSCFG
>  	  bus. System Configuration interface is one of the possible means
>  	  of generating transactions on this bus.
>  
> +config ASPEED_P2A_CTRL
> +	depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP && MFD_SYSCON
> +	tristate "Aspeed ast2400/2500 HOST P2A VGA MMIO to BMC bridge control"
> +	help
> +	  Control Aspeed ast2400/2500 HOST P2A VGA MMIO to BMC mappings 
> through
> +	  ioctl()s, the driver also provides an interface for userspace 
> mappings to
> +	  a pre-defined region.
> +
>  config ASPEED_LPC_CTRL
>  	depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP && MFD_SYSCON
>  	tristate "Aspeed ast2400/2500 HOST LPC to BMC bridge control"
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index e39ccbbc1b3a..57577aee354f 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -55,6 +55,7 @@ obj-$(CONFIG_VEXPRESS_SYSCFG)	+= vexpress-syscfg.o
>  obj-$(CONFIG_CXL_BASE)		+= cxl/
>  obj-$(CONFIG_ASPEED_LPC_CTRL)	+= aspeed-lpc-ctrl.o
>  obj-$(CONFIG_ASPEED_LPC_SNOOP)	+= aspeed-lpc-snoop.o
> +obj-$(CONFIG_ASPEED_P2A_CTRL)	+= aspeed-p2a-ctrl.o
>  obj-$(CONFIG_PCI_ENDPOINT_TEST)	+= pci_endpoint_test.o
>  obj-$(CONFIG_OCXL)		+= ocxl/
>  obj-y				+= cardreader/
> diff --git a/drivers/misc/aspeed-p2a-ctrl.c 
> b/drivers/misc/aspeed-p2a-ctrl.c
> new file mode 100644
> index 000000000000..6bde4f64632d
> --- /dev/null
> +++ b/drivers/misc/aspeed-p2a-ctrl.c
> @@ -0,0 +1,456 @@
> +/*
> + * Copyright 2019 Google Inc
> + *
> + * 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.

Should be a SPDX header instead.

> + *
> + * Provides a simple driver to control the ASPEED P2A interface which 
> allows
> + * the host to read and write to various regions of the BMC's memory.
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/io.h>
> +#include <linux/mfd/syscon.h>
> +#include <linux/miscdevice.h>
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/of_address.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +
> +#include <linux/aspeed-p2a-ctrl.h>
> +
> +#define DEVICE_NAME	"aspeed-p2a-ctrl"
> +
> +/* SCU2C is a Misc. Control Register. */
> +#define SCU2C 0x2c
> +/* SCU180 is the PCIe Configuration Setting Control Register. */
> +#define SCU180 0x180
> +/* Bit 1 controls the P2A bridge, while bit 0 controls the entire VGA 
> device
> + * on the PCI bus. */

As this wraps to multiple lines the trailing `*/` should be on a separate line.
There are a few instances of this throughout.

> +#define SCU180_ENP2A BIT(1)
> +
> +/* The ast2400/2500 both have six ranges. */
> +#define P2A_REGION_COUNT 6
> +
> +struct region {
> +	u32 min;
> +	u32 max;
> +	u32 bit;
> +};
> +
> +struct aspeed_p2a_model_data {
> +	/* min, max, bit */
> +	struct region regions[P2A_REGION_COUNT];
> +};
> +
> +struct aspeed_p2a_ctrl {
> +	struct miscdevice miscdev;
> +	struct regmap *regmap;
> +
> +	const struct aspeed_p2a_model_data *config;
> +
> +	/* Access to these needs to be locked, held via probe, mapping ioctl,
> +	 * and release, remove.
> +	 */
> +	struct mutex tracking;
> +	u32 readers;
> +	u32 readerwriters[P2A_REGION_COUNT];
> +
> +	phys_addr_t mem_base;
> +	resource_size_t mem_size;
> +};
> +
> +struct aspeed_p2a_user {
> +	struct file *file;
> +	struct aspeed_p2a_ctrl *parent;
> +
> +	/** The entire memory space is opened for reading once the bridge is
> +	 * enabled, therefore this needs only to be tracked once per user.
> +	 * If any user has it open for read, the bridge must stay enabled.
> +	 */

Generally the descriptions for the members are described in a kerneldoc
comment above the struct definition. Also you're mixing the kernel-doc
comment opener (`/**`) with non-kernel-doc comments (`/*` on the
tracking` mutex in `struct aspeed_p2a_ctrl` above).

> +	u32 read;
> +
> +	/** Each entry of the array corresponds to a P2A Region.  If the user
> +	 * opens for read or readwrite, the reference goes up here.  On 
> release,
> +	 * this array is walked and references adjusted accordingly.
> +	 */
> +	u32 readwrite[P2A_REGION_COUNT];
> +};
> +
> +static void aspeed_p2a_enable_bridge(struct aspeed_p2a_ctrl *p2a_ctrl)
> +{
> +	regmap_update_bits(p2a_ctrl->regmap, SCU180, SCU180_ENP2A, 
> SCU180_ENP2A);

Wrap this at 80 chars.

> +}
> +
> +static void aspeed_p2a_disable_bridge(struct aspeed_p2a_ctrl *p2a_ctrl)
> +{
> +	regmap_update_bits(p2a_ctrl->regmap, SCU180, SCU180_ENP2A, 0);
> +}
> +
> +static int aspeed_p2a_mmap(struct file *file, struct vm_area_struct 
> *vma)
> +{
> +	struct aspeed_p2a_user *priv = file->private_data;
> +	struct aspeed_p2a_ctrl *ctrl = priv->parent;
> +
> +	if (ctrl->mem_base == 0 && ctrl->mem_size == 0)
> +		return -EINVAL;
> +
> +	unsigned long vsize = vma->vm_end - vma->vm_start;
> +	pgprot_t prot = vma->vm_page_prot;
> +
> +	if (vma->vm_pgoff + vsize > ctrl->mem_base + ctrl->mem_size)
> +		return -EINVAL;
> +
> +	/* ast2400/2500 AHB accesses are not cache coherent */
> +	prot = pgprot_noncached(prot);
> +
> +	if (remap_pfn_range(vma, vma->vm_start,
> +		(ctrl->mem_base >> PAGE_SHIFT) + vma->vm_pgoff,
> +		vsize, prot))
> +		return -EAGAIN;
> +
> +	return 0;
> +}
> +
> +static void aspeed_p2a_region_acquire(struct aspeed_p2a_user *priv,
> +		struct aspeed_p2a_ctrl *ctrl,
> +		struct aspeed_p2a_ctrl_mapping *map)
> +{
> +	int i;
> +	u32 base, end;
> +
> +	base = map->addr;
> +	end = map->addr + (map->length - 1);
> +
> +	/* If the value is a legal u32, it will find a match. */
> +	for (i = 0; i < P2A_REGION_COUNT; i++) {
> +		const struct region *curr = &ctrl->config->regions[i];
> +
> +		/* If the top of this region is lower than your base, skip it.
> +		 */
> +		if (curr->max < base)
> +			continue;
> +
> +		/* If the bottom of this region is higher than your end, bail.
> +		 */
> +		if (curr->min > end)
> +			break;
> +		/* Lock this and update it, therefore it someone else is
> +		 * closing their file out, this'll preserve the increment.
> +		 */
> +		mutex_lock(&ctrl->tracking);
> +		ctrl->readerwriters[i] += 1;
> +		mutex_unlock(&ctrl->tracking);
> +
> +		/* Track with the user, so when they close their file, we can
> +		 * decrement properly.
> +		 */

The comments about tracking for decrement-on-release purposes is
useful, but I think the other comments in this loop are probably
unnecessary. Up to you though.

> +		priv->readwrite[i] += 1;
> +
> +		/* Enable the region as read-write. */
> +		regmap_update_bits(ctrl->regmap, SCU2C, curr->bit, 0);
> +	}
> +}
> +
> +static long aspeed_p2a_ioctl(struct file *file, unsigned int cmd,
> +		unsigned long data)
> +{
> +	struct aspeed_p2a_user *priv = file->private_data;
> +	struct aspeed_p2a_ctrl *ctrl = priv->parent;
> +	void __user *arg = (void __user *)data;
> +	struct aspeed_p2a_ctrl_mapping map;
> +
> +	if (copy_from_user(&map, arg, sizeof(map)))
> +		return -EFAULT;
> +
> +	switch (cmd) {
> +	case ASPEED_P2A_CTRL_IOCTL_SET_WINDOW:
> +		/* If they want a region to be read-only, since the entire
> +		 * region is read-only once enabled, we just need to track this
> +		 * user wants to read from the bridge, and if it's not enabled.
> +		 * Enable it.
> +		 */
> +		if (map.flags == ASPEED_P2A_CTRL_READ_ONLY) {
> +			mutex_lock(&ctrl->tracking);
> +			ctrl->readers += 1;
> +			mutex_unlock(&ctrl->tracking);
> +
> +			/* Track with the user, so when they close their file,
> +			 * we can decrement properly.
> +			 */
> +			priv->read += 1;
> +		} else if (map.flags == ASPEED_P2A_CTRL_READWRITE) {
> +			aspeed_p2a_region_acquire(priv, ctrl, &map);
> +		} else {
> +			/* Invalid map flags. */
> +			return -EINVAL;
> +		}
> +
> +		aspeed_p2a_enable_bridge(ctrl);
> +		return 0;
> +	case ASPEED_P2A_CTRL_IOCTL_GET_MEMORY_CONFIG:
> +		/* This is a request for the memory-region and corresponding
> +		 * length that is used by the driver for mmap. */
> +
> +		map.flags = 0;
> +		map.addr = ctrl->mem_base;
> +		map.length = ctrl->mem_size;

Thinking out loud here - do we want to allow ourselves an escape hatch
for supporting multiple reserved memory locations? Otherwise we might
need a new ioctl() for it. On the flip-side, not actually having this use-case
means we might break the implementation anyway, so it could be a
double-edged sword. Thoughts?

> +
> +		return copy_to_user(arg, &map, sizeof(map)) ? -EFAULT : 0;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +
> +/**
> + * When a user opens this file, we create a structure to track their 
> mappings.
> + *
> + * A user can map a region as read-only (bridge enabled), or 
> read-write (bit
> + * flipped, and bridge enabled).  Either way, this tracking is used, 
> s.t. when
> + * they release the device references are handled.
> + *
> + * The bridge is not enabled until a user calls an ioctl to map a 
> region,
> + * simply opening the device does not enable it.
> + */
> +static int aspeed_p2a_open(struct inode *inode, struct file *file)
> +{
> +	struct aspeed_p2a_user *priv;
> +
> +	priv = kmalloc(sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->file = file;
> +	priv->read = 0;
> +	memset(priv->readwrite, 0, sizeof(priv->readwrite));
> +
> +	/* The file's private_data is initialized to the p2a_ctrl. */
> +	priv->parent = file->private_data;
> +
> +	/* Set the file's private_data to the user's data. */
> +	file->private_data = priv;
> +
> +	return 0;
> +}
> +
> +/**
> + * This will close the users mappings.  It will go through what they 
> had opened
> + * for readwrite, and decrement those counts.  If at the end, this is 
> the last
> + * user, it'll close the bridge.
> + */
> +static int aspeed_p2a_release(struct inode *inode, struct file *file)
> +{
> +	int i;
> +	u32 value;
> +	u32 bits = 0;
> +	bool open_regions = false;
> +	struct aspeed_p2a_user *priv = file->private_data;
> +
> +	/* Lock others from changing these values until everything is updated
> +	 * in one pass */
> +	mutex_lock(&priv->parent->tracking);
> +
> +	priv->parent->readers -= priv->read;;
> +
> +	for (i = 0; i < P2A_REGION_COUNT; i++) {
> +		priv->parent->readerwriters[i] -= priv->readwrite[i];
> +
> +		if (priv->parent->readerwriters[i] > 0)
> +			open_regions = true;
> +		else
> +			bits |= priv->parent->config->regions[i].bit;
> +	}
> +
> +	/* Setting a bit to 1 disables the region, so let's just OR with the
> +	 * above to disable any.
> +	 */
> +
> +	/* Note, if another user is trying to ioctl, they can't grab tracking,
> +	 * and therefore can't grab either register mutex.
> +	 * If another user is trying to close, they can't grab tracking 
> either.
> +	 */
> +	regmap_update_bits(priv->parent->regmap, SCU2C, bits, bits);
> +
> +	/* If parent->readers is zero and open windows is 0, disable the
> +	 * bridge.
> +	 */
> +	if (!open_regions && priv->parent->readers == 0)
> +		aspeed_p2a_disable_bridge(priv->parent);
> +
> +	mutex_unlock(&priv->parent->tracking);
> +
> +	kfree(priv);
> +
> +	return 0;
> +}
> +
> +static const struct file_operations aspeed_p2a_ctrl_fops = {
> +	.owner = THIS_MODULE,
> +	.mmap = aspeed_p2a_mmap,
> +	.unlocked_ioctl = aspeed_p2a_ioctl,
> +	.open = aspeed_p2a_open,
> +	.release = aspeed_p2a_release,
> +};
> +
> +/** The regions are controlled by SCU2C */
> +static void aspeed_p2a_disable_all(struct aspeed_p2a_ctrl *p2a_ctrl)
> +{
> +	int i;
> +	u32 value = 0;
> +
> +	for (i = 0; i < P2A_REGION_COUNT; i++)
> +		value |= p2a_ctrl->config->regions[i].bit;
> +
> +	regmap_update_bits(p2a_ctrl->regmap, SCU2C, value, value);
> +
> +	/* Disable the bridge. */
> +	aspeed_p2a_disable_bridge(p2a_ctrl);
> +}
> +
> +static int aspeed_p2a_ctrl_probe(struct platform_device *pdev)
> +{
> +	struct aspeed_p2a_ctrl *misc_ctrl;
> +	struct device *dev;
> +	struct resource *res, resm;
> +	struct device_node *node;
> +	int rc = 0;
> +
> +	dev = &pdev->dev;
> +
> +	misc_ctrl = devm_kzalloc(dev, sizeof(*misc_ctrl), GFP_KERNEL);
> +	if (!misc_ctrl)
> +		return -ENOMEM;
> +
> +	mutex_init(&misc_ctrl->tracking);
> +	misc_ctrl->readers = 0;
> +	memset(misc_ctrl->readerwriters, 0, sizeof(misc_ctrl->readerwriters));
> +
> +	misc_ctrl->mem_size = 0;
> +	misc_ctrl->mem_base = 0;
> +
> +	/* optional. */
> +	node = of_parse_phandle(dev->of_node, "memory-region", 0);
> +	if (node) {
> +		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");

I think the message could be improved, something like "No reserved memory
specified". Having said that, I don't think it should be an error condition either;
our experience with aspeed-lpc-ctrl was that it was useful for the memory-region
property to be optional. You already have:

> +
> +	if (ctrl->mem_base == 0 && ctrl->mem_size == 0)
> +		return -EINVAL;

in the mmap() callback, but we don't get that far unless someone has specified a
zero-sized reserved-memory node. I think supporting memory-region as optional
is just a matter of adding the same check to the GET_MEMORY_CONFIG ioctl().

> +			return -ENOMEM;

The system isn't out of memory so this isn't an ENOMEM condition. I think ENODEV
is more appropriate, but if we make the memory region optional then this goes
away anyway.

> +		}
> +
> +		misc_ctrl->mem_size = resource_size(&resm);
> +		misc_ctrl->mem_base = resm.start;
> +	}
> +
> +	node = of_parse_phandle(dev->of_node, "syscon", 0);
> +	if (!node) {
> +		dev_err(dev, "Couldn't find syscon property\n");
> +		return -ENODEV;
> +	}
> +
> +	misc_ctrl->regmap = syscon_node_to_regmap(node);
> +	if (IS_ERR(misc_ctrl->regmap)) {
> +		dev_err(dev, "Couldn't get regmap\n");
> +		return -ENODEV;
> +	}
> +	of_node_put(node);
> +
> +	misc_ctrl->config = of_device_get_match_data(dev);
> +
> +	dev_set_drvdata(&pdev->dev, misc_ctrl);
> +
> +	aspeed_p2a_disable_all(misc_ctrl);
> +
> +	misc_ctrl->miscdev.minor = MISC_DYNAMIC_MINOR;
> +	misc_ctrl->miscdev.name = DEVICE_NAME;
> +	misc_ctrl->miscdev.fops = &aspeed_p2a_ctrl_fops;
> +	misc_ctrl->miscdev.parent = dev;
> +
> +	rc = misc_register(&misc_ctrl->miscdev);
> +	if (rc)
> +		dev_err(dev, "Unable to register device\n");
> +
> +	return rc;
> +}
> +
> +static int aspeed_p2a_ctrl_remove(struct platform_device *pdev)
> +{
> +	struct aspeed_p2a_ctrl *p2a_ctrl = dev_get_drvdata(&pdev->dev);
> +
> +	misc_deregister(&p2a_ctrl->miscdev);
> +
> +	return 0;
> +}
> +
> +/*
> + * bit | SCU2C | ast2400
> + *  25 | DRAM  | 0x40000000 - 0x5FFFFFFF
> + *  24 | SPI   | 0x30000000 - 0x3FFFFFFF
> + *  23 | SOC   | 0x18000000 - 0x1FFFFFFF, 0x60000000 - 0xFFFFFFFF
> + *  22 | FLASH | 0x00000000 - 0x17FFFFFF, 0x20000000 - 0x2FFFFFFF
> + *
> + * bit | SCU2C | ast2500
> + *  25 | DRAM  | 0x80000000 - 0xFFFFFFFF
> + *  24 | SPI   | 0x60000000 - 0x7FFFFFFF
> + *  23 | SOC   | 0x10000000 - 0x1FFFFFFF, 0x40000000 - 0x5FFFFFFF
> + *  22 | FLASH | 0x00000000 - 0x0FFFFFFF, 0x20000000 - 0x3FFFFFFF
> + */

The comment is probably unnecessary given the structure declarations
below.

> +
> +#define SCU2C_DRAM	BIT(25)
> +#define SCU2C_SPI	BIT(24)
> +#define SCU2C_SOC	BIT(23)
> +#define SCU2C_FLASH	BIT(22)
> +
> +static const struct aspeed_p2a_model_data ast2400_model_data = {
> +	.regions = {
> +		{0x00000000, 0x17FFFFFF, SCU2C_FLASH},
> +		{0x18000000, 0x1FFFFFFF, SCU2C_SOC},
> +		{0x20000000, 0x2FFFFFFF, SCU2C_FLASH},
> +		{0x30000000, 0x3FFFFFFF, SCU2C_SPI},
> +		{0x40000000, 0x5FFFFFFF, SCU2C_DRAM},
> +		{0x60000000, 0xFFFFFFFF, SCU2C_SOC},
> +	}
> +};
> +
> +static const struct aspeed_p2a_model_data ast2500_model_data = {
> +	.regions = {
> +		{0x00000000, 0x0FFFFFFF, SCU2C_FLASH},
> +		{0x10000000, 0x1FFFFFFF, SCU2C_SOC},
> +		{0x20000000, 0x3FFFFFFF, SCU2C_FLASH},
> +		{0x40000000, 0x5FFFFFFF, SCU2C_SOC},
> +		{0x60000000, 0x7FFFFFFF, SCU2C_SPI},
> +		{0x80000000, 0xFFFFFFFF, SCU2C_DRAM},
> +	}
> +};
> +
> +static const struct of_device_id aspeed_p2a_ctrl_match[] = {
> +	{ .compatible = "aspeed,ast2400-p2a-ctrl",
> +	  .data = &ast2400_model_data },
> +	{ .compatible = "aspeed,ast2500-p2a-ctrl",
> +	  .data = &ast2500_model_data },
> +	{ },
> +};
> +
> +static struct platform_driver aspeed_p2a_ctrl_driver = {
> +	.driver = {
> +		.name		= DEVICE_NAME,
> +		.of_match_table = aspeed_p2a_ctrl_match,
> +	},
> +	.probe = aspeed_p2a_ctrl_probe,
> +	.remove = aspeed_p2a_ctrl_remove,
> +};
> +
> +module_platform_driver(aspeed_p2a_ctrl_driver);
> +
> +MODULE_DEVICE_TABLE(of, aspeed_p2a_ctrl_match);
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Patrick Venture <venture@xxxxxxxxxx>");
> +MODULE_DESCRIPTION("Control for aspeed 2400/2500 P2A VGA HOST to BMC 
> mappings");
> diff --git a/include/uapi/linux/aspeed-p2a-ctrl.h 
> b/include/uapi/linux/aspeed-p2a-ctrl.h
> new file mode 100644
> index 000000000000..e839cdc31db9
> --- /dev/null
> +++ b/include/uapi/linux/aspeed-p2a-ctrl.h
> @@ -0,0 +1,59 @@
> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> +/*
> + * Copyright 2019 Google Inc
> + *
> + * 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.

SPDX again.

> + *
> + * Provides a simple driver to control the ASPEED P2A interface which 
> allows
> + * the host to read and write to various regions of the BMC's memory.
> + */
> +
> +#ifndef _UAPI_LINUX_ASPEED_P2A_CTRL_H
> +#define _UAPI_LINUX_ASPEED_P2A_CTRL_H
> +
> +#include <linux/ioctl.h>
> +#include <linux/types.h>
> +
> +#define ASPEED_P2A_CTRL_READ_ONLY 0
> +#define ASPEED_P2A_CTRL_READWRITE 1
> +
> +/*
> + * This driver provides a mechanism for enabling or disabling the 
> read-write
> + * property of specific windows into the ASPEED BMC's memory.
> + *
> + * A user can map a region of the BMC's memory as read-only or 
> read-write, with
> + * the caveat that once any region is mapped, all regions are unlocked 
> for
> + * reading.
> + */
> +
> +/**
> + * Unlock a region of BMC physical memory for access from the host.
> + *
> + * Also used to read back the optional memory-region configuration for 
> the
> + * driver.
> + */
> +struct aspeed_p2a_ctrl_mapping {
> +	__u32 addr;
> +	__u32 length;
> +	__u32 flags;
> +};
> +
> +#define __ASPEED_P2A_CTRL_IOCTL_MAGIC 0xb3
> +
> +/**
> + * This IOCTL is meant to configure a region or regions of memory 
> given a
> + * starting address and length to be readable by the host, or
> + * readable-writeable. */
> +#define ASPEED_P2A_CTRL_IOCTL_SET_WINDOW 
> _IOW(__ASPEED_P2A_CTRL_IOCTL_MAGIC, \
> +		0x00, struct aspeed_p2a_ctrl_mapping)
> +
> +/**
> + * This IOCTL is meant to read back to the user the base address and 
> length of
> + * the memory-region specified to the driver for use with mmap. */
> +#define ASPEED_P2A_CTRL_IOCTL_GET_MEMORY_CONFIG 
> _IOWR(__ASPEED_P2A_CTRL_IOCTL_MAGIC, \

Wrap this at 80?

Cheers,

Andrew

> +		0x01, struct aspeed_p2a_ctrl_mapping)
> +
> +#endif /* _UAPI_LINUX_ASPEED_P2A_CTRL_H */
> -- 
> 2.21.0.rc2.261.ga7da99ff1b-goog
> 
>