fpga: dfl: support multiple opens on feature device node.

Each DFL functional block, e.g. AFU (Accelerated Function Unit) and FME
(FPGA Management Engine), could implement more than one function within
its region, but current driver only allows one user application to access
it by exclusive open on device node. So this is not convenient and
flexible for userspace applications, as they have to combine lots of
different functions into one single application.

This patch removes the limitation here to allow multiple opens to each
feature device node for AFU and FME from userspace applications. If user
still needs exclusive access to these device node, O_EXCL flag must be
issued together with open.

Signed-off-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

1 files changed, 27 insertions, 8 deletions

diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h
index 9f0e656de720..4a9a33cd9979 100644
--- a/drivers/fpga/dfl.h
+++ b/drivers/fpga/dfl.h
@@ -205,8 +205,6 @@ struct dfl_feature {
 	const struct dfl_feature_ops *ops;
 };
 
-#define DEV_STATUS_IN_USE	0
-
 #define FEATURE_DEV_ID_UNUSED	(-1)
 
 /**
@@ -219,8 +217,9 @@ struct dfl_feature {
  * @dfl_cdev: ptr to container device.
  * @id: id used for this feature device.
  * @disable_count: count for port disable.
+ * @excl_open: set on feature device exclusive open.
+ * @open_count: count for feature device open.
  * @num: number for sub features.
- * @dev_status: dev status (e.g. DEV_STATUS_IN_USE).
  * @private: ptr to feature dev private data.
  * @features: sub features of this feature dev.
  */
@@ -232,26 +231,46 @@ struct dfl_feature_platform_data {
 	struct dfl_fpga_cdev *dfl_cdev;
 	int id;
 	unsigned int disable_count;
-	unsigned long dev_status;
+	bool excl_open;
+	int open_count;
 	void *private;
 	int num;
 	struct dfl_feature features[0];
 };
 
 static inline
-int dfl_feature_dev_use_begin(struct dfl_feature_platform_data *pdata)
+int dfl_feature_dev_use_begin(struct dfl_feature_platform_data *pdata,
+			      bool excl)
 {
-	/* Test and set IN_USE flags to ensure file is exclusively used */
-	if (test_and_set_bit_lock(DEV_STATUS_IN_USE, &pdata->dev_status))
+	if (pdata->excl_open)
 		return -EBUSY;
 
+	if (excl) {
+		if (pdata->open_count)
+			return -EBUSY;
+
+		pdata->excl_open = true;
+	}
+	pdata->open_count++;
+
 	return 0;
 }
 
 static inline
 void dfl_feature_dev_use_end(struct dfl_feature_platform_data *pdata)
 {
-	clear_bit_unlock(DEV_STATUS_IN_USE, &pdata->dev_status);
+	pdata->excl_open = false;
+
+	if (WARN_ON(pdata->open_count <= 0))
+		return;
+
+	pdata->open_count--;
+}
+
+static inline
+int dfl_feature_dev_use_count(struct dfl_feature_platform_data *pdata)
+{
+	return pdata->open_count;
 }
 
 static inline