accel/qaic: Add fifo size debugfs

Each DMA Bridge Channel (dbc) has a unique configured fifo size which is
specified by the userspace client of that dbc. Since the fifo is
circular, it is useful to know the configured size when debugging
issues.

Add a per-dbc subdirectory in debugfs and in each subdirectory add a
fifo_size entry that will display the size of that dbc's fifo when read.

Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Reviewed-by: Carl Vanderlip <quic_carlv@quicinc.com>
Reviewed-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com>
Reviewed-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240322175730.3855440-3-quic_jhugo@quicinc.com

Author: quic-jhugo

drivers/accel/qaic/qaic_debugfs.c

@@ -12,6 +12,7 @@
 #include <linux/overflow.h>
 #include <linux/pci.h>
 #include <linux/seq_file.h>
+#include <linux/sprintf.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
@@ -21,6 +22,7 @@
 
 #define BOOTLOG_POOL_SIZE		16
 #define BOOTLOG_MSG_SIZE		512
+#define QAIC_DBC_DIR_NAME		9
 
 struct bootlog_msg {
 	/* Buffer for bootlog messages */
@@ -75,14 +77,47 @@ static const struct file_operations bootlog_fops = {
 	.release = single_release,
 };
 
+static int read_dbc_fifo_size(struct seq_file *s, void *unused)
+{
+	struct dma_bridge_chan *dbc = s->private;
+
+	seq_printf(s, "%u\n", dbc->nelem);
+	return 0;
+}
+
+static int fifo_size_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, read_dbc_fifo_size, inode->i_private);
+}
+
+static const struct file_operations fifo_size_fops = {
+	.owner = THIS_MODULE,
+	.open = fifo_size_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+};
+
 void qaic_debugfs_init(struct qaic_drm_device *qddev)
 {
 	struct qaic_device *qdev = qddev->qdev;
 	struct dentry *debugfs_root;
+	struct dentry *debugfs_dir;
+	char name[QAIC_DBC_DIR_NAME];
+	u32 i;
 
 	debugfs_root = to_drm(qddev)->debugfs_root;
 
 	debugfs_create_file("bootlog", 0400, debugfs_root, qdev, &bootlog_fops);
+	/*
+	 * 256 dbcs per device is likely the max we will ever see and lets static checking see a
+	 * reasonable range.
+	 */
+	for (i = 0; i < qdev->num_dbc && i < 256; ++i) {
+		snprintf(name, QAIC_DBC_DIR_NAME, "dbc%03u", i);
+		debugfs_dir = debugfs_create_dir(name, debugfs_root);
+		debugfs_create_file("fifo_size", 0400, debugfs_dir, &qdev->dbc[i], &fifo_size_fops);
+	}
 }
 
 static struct bootlog_page *alloc_bootlog_page(struct qaic_device *qdev)