fpga: region: add compat_id support

This patch introduces a compat_id pointer member and sysfs interface
for each fpga region, similar as compat_id for fpga manager, it allows
applications to read the per region compat_id for compatibility
checking before other actions on this fpga-region (e.g. PR).

Signed-off-by: Wu Hao <[e-mail]>
Acked-by: Alan Tull <[e-mail]>
Acked-by: Moritz Fischer <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-class-fpga-region

···
+What:		/sys/class/fpga_region/<region>/compat_id
+Date:		June 2018
+KernelVersion:	4.19
+Contact:	Wu Hao <[e-mail]>
+Description:	FPGA region id for compatibility check, e.g. compatibility
+		of the FPGA reconfiguration hardware and image. This value
+		is defined or calculated by the layer that is creating the
+		FPGA region. This interface returns the compat_id value or
+		just error code -ENOENT in case compat_id is not used.

drivers/fpga/fpga-region.c

···
 }
 EXPORT_SYMBOL_GPL(fpga_region_program_fpga);
 
+static ssize_t compat_id_show(struct device *dev,
+			      struct device_attribute *attr, char *buf)
+{
+	struct fpga_region *region = to_fpga_region(dev);
+
+	if (!region->compat_id)
+		return -ENOENT;
+
+	return sprintf(buf, "%016llx%016llx\n",
+		       (unsigned long long)region->compat_id->id_h,
+		       (unsigned long long)region->compat_id->id_l);
+}
+
+static DEVICE_ATTR_RO(compat_id);
+
+static struct attribute *fpga_region_attrs[] = {
+	&dev_attr_compat_id.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(fpga_region);
+
 /**
  * fpga_region_create - alloc and init a struct fpga_region
  * @dev: device parent
···
 	if (IS_ERR(fpga_region_class))
 		return PTR_ERR(fpga_region_class);
 
+	fpga_region_class->dev_groups = fpga_region_groups;
 	fpga_region_class->dev_release = fpga_region_dev_release;
 
 	return 0;

include/linux/fpga/fpga-region.h

···
  * @bridge_list: list of FPGA bridges specified in region
  * @mgr: FPGA manager
  * @info: FPGA image info
+ * @compat_id: FPGA region id for compatibility check.
  * @priv: private data
  * @get_bridges: optional function to get bridges to a list
  */
···
 	struct list_head bridge_list;
 	struct fpga_manager *mgr;
 	struct fpga_image_info *info;
+	struct fpga_compat_id *compat_id;
 	void *priv;
 	int (*get_bridges)(struct fpga_region *region);
 };