fpga: support loading from a pre-allocated buffer

Some systems are memory constrained but they need to load very
large Configuration files. The FPGA subsystem allows drivers to
request this Configuration image be loaded from the filesystem,
but this requires that the entire configuration data be loaded
into kernel memory first before it's provided to the driver.
This can lead to a situation where we map the configuration
data twice, once to load the configuration data into kernel
memory and once to copy the configuration data into the final
resting place which is nothing but a dma-able continuous buffer.

This creates needless memory pressure and delays due to multiple
copies. Let's add a dmabuf handling support to the fpga manager
framework that allows drivers to load the Configuration data
directly from a pre-allocated buffer. This skips the intermediate
step of allocating a buffer in kernel memory to hold the
Configuration data.

Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
State: pending

drivers/fpga/fpga-mgr.c

@@ -8,6 +8,8 @@
  * With code from the mailing list:
  * Copyright (C) 2013 Xilinx, Inc.
  */
+#include <linux/dma-buf.h>
+#include <linux/dma-map-ops.h>
 #include <linux/kernel.h>
 #include <linux/firmware.h>
 #include <linux/fpga/fpga-mgr.h>
@@ -352,6 +354,39 @@ static int fpga_mgr_buf_load(struct fpga_manager *mgr,
 	return rc;
 }
 
+static int fpga_dmabuf_load(struct fpga_manager *mgr,
+			    struct fpga_image_info *info)
+{
+	struct dma_buf_attachment *attach;
+	struct sg_table *sgt;
+	int ret;
+
+	/* create attachment for dmabuf with the user device */
+	attach = dma_buf_attach(mgr->dmabuf, &mgr->dev);
+	if (IS_ERR(attach)) {
+		pr_err("failed to attach dmabuf\n");
+		ret = PTR_ERR(attach);
+		goto fail_put;
+	}
+
+	sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
+	if (IS_ERR(sgt)) {
+		ret = PTR_ERR(sgt);
+		goto fail_detach;
+	}
+
+	info->sgt = sgt;
+	ret = fpga_mgr_buf_load_sg(mgr, info, info->sgt);
+	dma_buf_unmap_attachment(attach, sgt, DMA_BIDIRECTIONAL);
+
+fail_detach:
+	dma_buf_detach(mgr->dmabuf, attach);
+fail_put:
+	dma_buf_put(mgr->dmabuf);
+
+	return ret;
+}
+
 /**
  * fpga_mgr_firmware_load - request firmware and load to fpga
  * @mgr:	fpga manager
@@ -408,6 +443,8 @@ static int fpga_mgr_firmware_load(struct fpga_manager *mgr,
  */
 int fpga_mgr_load(struct fpga_manager *mgr, struct fpga_image_info *info)
 {
+	if (mgr->flags & FPGA_MGR_CONFIG_DMA_BUF)
+		return fpga_dmabuf_load(mgr, info);
 	if (info->sgt)
 		return fpga_mgr_buf_load_sg(mgr, info, info->sgt);
 	if (info->buf && info->count)
@@ -692,6 +729,64 @@ static const struct file_operations fpga_mgr_ops_image = {
 };
 #endif
 
+static int fpga_dmabuf_fd_get(struct file *file, char __user *argp)
+{
+	struct fpga_manager *mgr =  (struct fpga_manager *)(file->private_data);
+	int buffd;
+
+	if (copy_from_user(&buffd, argp, sizeof(buffd)))
+		return -EFAULT;
+
+	mgr->dmabuf = dma_buf_get(buffd);
+	if (IS_ERR_OR_NULL(mgr->dmabuf))
+		return -EINVAL;
+
+	mgr->flags = FPGA_MGR_CONFIG_DMA_BUF;
+
+	return 0;
+}
+
+static int fpga_device_open(struct inode *inode, struct file *file)
+{
+	struct miscdevice *miscdev = file->private_data;
+	struct fpga_manager *mgr = container_of(miscdev,
+						struct fpga_manager, miscdev);
+
+	file->private_data = mgr;
+
+	return 0;
+}
+
+static int fpga_device_release(struct inode *inode, struct file *file)
+{
+	return 0;
+}
+
+static long fpga_device_ioctl(struct file *file, unsigned int cmd,
+			      unsigned long arg)
+{
+	char __user *argp = (char __user *)arg;
+	int err;
+
+	switch (cmd) {
+	case FPGA_IOCTL_LOAD_DMA_BUFF:
+		err = fpga_dmabuf_fd_get(file, argp);
+		break;
+	default:
+		err = -ENOTTY;
+	}
+
+	return err;
+}
+
+static const struct file_operations fpga_fops = {
+	.owner		= THIS_MODULE,
+	.open		= fpga_device_open,
+	.release	= fpga_device_release,
+	.unlocked_ioctl	= fpga_device_ioctl,
+	.compat_ioctl	= fpga_device_ioctl,
+};
+
 /**
  * fpga_mgr_lock - Lock FPGA manager for exclusive use
  * @mgr:	fpga manager
@@ -775,10 +870,28 @@ struct fpga_manager *fpga_mgr_create(struct device *parent, const char *name,
 	mgr->dev.of_node = parent->of_node;
 	mgr->dev.id = id;
 
+	/* Make device dma capable by inheriting from parent's */
+	set_dma_ops(&mgr->dev, get_dma_ops(parent));
+	ret = dma_coerce_mask_and_coherent(&mgr->dev, dma_get_mask(parent));
+	if (ret) {
+		dev_warn(parent,
+			 "Failed to set DMA mask %llx. Trying to continue... %x\n",
+			 dma_get_mask(parent), ret);
+	}
+
 	ret = dev_set_name(&mgr->dev, "fpga%d", id);
 	if (ret)
 		goto error_device;
 
+	mgr->miscdev.minor = MISC_DYNAMIC_MINOR;
+	mgr->miscdev.name = kobject_name(&mgr->dev.kobj);
+	mgr->miscdev.fops = &fpga_fops;
+	ret = misc_register(&mgr->miscdev);
+	if (ret) {
+		pr_err("fpga: failed to register misc device.\n");
+		goto error_device;
+	}
+
 	return mgr;
 
 error_device:

include/linux/fpga/fpga-mgr.h

@@ -9,6 +9,7 @@
 #define _LINUX_FPGA_MGR_H
 
 #include <linux/mutex.h>
+#include <linux/miscdevice.h>
 #include <linux/platform_device.h>
 
 #define ENCRYPTED_KEY_LEN	64 /* Bytes */
@@ -86,6 +87,7 @@ enum fpga_mgr_states {
 #define FPGA_MGR_USERKEY_ENCRYPTED_BITSTREAM	BIT(5)
 #define FPGA_MGR_DDR_MEM_AUTH_BITSTREAM		BIT(6)
 #define FPGA_MGR_SECURE_MEM_AUTH_BITSTREAM	BIT(7)
+#define FPGA_MGR_CONFIG_DMA_BUF			BIT(8)
 
 /**
  * struct fpga_image_info - information specific to an FPGA image
@@ -195,6 +197,8 @@ struct fpga_manager {
 	unsigned long flags;
 	char key[ENCRYPTED_KEY_LEN + 1];
 	struct device dev;
+	struct miscdevice miscdev;
+	struct dma_buf *dmabuf;
 	struct mutex ref_mutex;
 	enum fpga_mgr_states state;
 	struct fpga_compat_id *compat_id;
@@ -235,4 +239,6 @@ struct fpga_manager *devm_fpga_mgr_create(struct device *dev, const char *name,
 					  const struct fpga_manager_ops *mops,
 					  void *priv);
 
+#define FPGA_IOCTL_LOAD_DMA_BUFF	_IOWR('R', 1, __u32)
+
 #endif /*_LINUX_FPGA_MGR_H */