drm/xe/eustall: Add support to read() and poll() EU stall data

Implement the EU stall sampling APIs to read() and poll() EU stall data.
A work function periodically polls the EU stall data buffer write pointer
registers to look for any new data and caches the write pointer. The read
function compares the cached read and write pointers and copies any new
data to the user space.

v11: Used gt->eu_stall->stream_lock instead of stream->buf_lock.
     Removed read and write offsets from trace and added read size.
     Moved workqueue from struct xe_eu_stall_data_stream to
     struct xe_eu_stall_gt.
v10: Used cancel_delayed_work_sync() instead of flush_delayed_work()
     Replaced per xecore lock with a lock for all the xecore buffers
     Code movement and optimizations as per review feedback
v9:  New patch split from the previous patch.
     Used *_delayed_work functions instead of hrtimer
     Addressed the review feedback in read and poll functions

Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Harish Chegondi <harish.chegondi@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/369dee85a3b6bd2c08aeae89ca55e66a9a0242d2.1740533885.git.harish.chegondi@intel.com

Author: harishchegondi

drivers/gpu/drm/xe/xe_eu_stall.c

@@ -21,10 +21,13 @@
 #include "xe_macros.h"
 #include "xe_observation.h"
 #include "xe_pm.h"
+#include "xe_trace.h"
 
 #include "regs/xe_eu_stall_regs.h"
 #include "regs/xe_gt_regs.h"
 
+#define POLL_PERIOD_MS	5
+
 static size_t per_xecore_buf_size = SZ_512K;
 
 struct per_xecore_buf {
@@ -37,22 +40,27 @@ struct per_xecore_buf {
 };
 
 struct xe_eu_stall_data_stream {
+	bool pollin;
 	bool enabled;
 	int wait_num_reports;
 	int sampling_rate_mult;
+	wait_queue_head_t poll_wq;
 	size_t data_record_size;
 	size_t per_xecore_buf_size;
 
 	struct xe_gt *gt;
 	struct xe_bo *bo;
 	struct per_xecore_buf *xecore_buf;
+	struct delayed_work buf_poll_work;
 };
 
 struct xe_eu_stall_gt {
 	/* Lock to protect stream */
 	struct mutex stream_lock;
 	/* EU stall data stream */
 	struct xe_eu_stall_data_stream *stream;
+	/* Workqueue to schedule buffer pointers polling work */
+	struct workqueue_struct *buf_ptr_poll_wq;
 };
 
 /**
@@ -114,6 +122,7 @@ static void xe_eu_stall_fini(void *arg)
 {
 	struct xe_gt *gt = arg;
 
+	destroy_workqueue(gt->eu_stall->buf_ptr_poll_wq);
 	mutex_destroy(&gt->eu_stall->stream_lock);
 	kfree(gt->eu_stall);
 }
@@ -139,11 +148,19 @@ int xe_eu_stall_init(struct xe_gt *gt)
 
 	mutex_init(&gt->eu_stall->stream_lock);
 
+	gt->eu_stall->buf_ptr_poll_wq = alloc_ordered_workqueue("xe_eu_stall", 0);
+	if (!gt->eu_stall->buf_ptr_poll_wq) {
+		ret = -ENOMEM;
+		goto exit_free;
+	}
+
 	ret = devm_add_action_or_reset(xe->drm.dev, xe_eu_stall_fini, gt);
 	if (ret)
-		goto exit_free;
+		goto exit_destroy;
 
 	return 0;
+exit_destroy:
+	destroy_workqueue(gt->eu_stall->buf_ptr_poll_wq);
 exit_free:
 	mutex_destroy(&gt->eu_stall->stream_lock);
 	kfree(gt->eu_stall);
@@ -248,14 +265,214 @@ static int xe_eu_stall_user_extensions(struct xe_device *xe, u64 extension,
 	return 0;
 }
 
+/**
+ * buf_data_size - Calculate the number of bytes in a circular buffer
+ *		   given the read and write pointers and the size of
+ *		   the buffer.
+ *
+ * @buf_size: Size of the circular buffer
+ * @read_ptr: Read pointer with an additional overflow bit
+ * @write_ptr: Write pointer with an additional overflow bit
+ *
+ * Since the read and write pointers have an additional overflow bit,
+ * this function calculates the offsets from the pointers and use the
+ * offsets to calculate the data size in the buffer.
+ *
+ * Returns: number of bytes of data in the buffer
+ */
+static u32 buf_data_size(size_t buf_size, u32 read_ptr, u32 write_ptr)
+{
+	u32 read_offset, write_offset, size = 0;
+
+	if (read_ptr == write_ptr)
+		goto exit;
+
+	read_offset = read_ptr & (buf_size - 1);
+	write_offset = write_ptr & (buf_size - 1);
+
+	if (write_offset > read_offset)
+		size = write_offset - read_offset;
+	else
+		size = buf_size - read_offset + write_offset;
+exit:
+	return size;
+}
+
+/**
+ * eu_stall_data_buf_poll - Poll for EU stall data in the buffer.
+ *
+ * @stream: xe EU stall data stream instance
+ *
+ * Returns: true if the EU stall buffer contains minimum stall data as
+ *	    specified by the event report count, else false.
+ */
+static bool eu_stall_data_buf_poll(struct xe_eu_stall_data_stream *stream)
+{
+	u32 read_ptr, write_ptr_reg, write_ptr, total_data = 0;
+	u32 buf_size = stream->per_xecore_buf_size;
+	struct per_xecore_buf *xecore_buf;
+	struct xe_gt *gt = stream->gt;
+	bool min_data_present = false;
+	u16 group, instance;
+	unsigned int xecore;
+
+	mutex_lock(&gt->eu_stall->stream_lock);
+	for_each_dss_steering(xecore, gt, group, instance) {
+		xecore_buf = &stream->xecore_buf[xecore];
+		read_ptr = xecore_buf->read;
+		write_ptr_reg = xe_gt_mcr_unicast_read(gt, XEHPC_EUSTALL_REPORT,
+						       group, instance);
+		write_ptr = REG_FIELD_GET(XEHPC_EUSTALL_REPORT_WRITE_PTR_MASK, write_ptr_reg);
+		write_ptr <<= 6;
+		write_ptr &= ((buf_size << 1) - 1);
+		if (!min_data_present) {
+			total_data += buf_data_size(buf_size, read_ptr, write_ptr);
+			if (num_data_rows(total_data) >= stream->wait_num_reports)
+				min_data_present = true;
+		}
+		xecore_buf->write = write_ptr;
+	}
+	mutex_unlock(&gt->eu_stall->stream_lock);
+
+	return min_data_present;
+}
+
+static int xe_eu_stall_data_buf_read(struct xe_eu_stall_data_stream *stream,
+				     char __user *buf, size_t count,
+				     size_t *total_data_size, struct xe_gt *gt,
+				     u16 group, u16 instance, unsigned int xecore)
+{
+	size_t read_data_size, copy_size, buf_size;
+	u32 read_ptr_reg, read_ptr, write_ptr;
+	u8 *xecore_start_vaddr, *read_vaddr;
+	struct per_xecore_buf *xecore_buf;
+	u32 read_offset, write_offset;
+
+	/* Hardware increments the read and write pointers such that they can
+	 * overflow into one additional bit. For example, a 256KB size buffer
+	 * offset pointer needs 18 bits. But HW uses 19 bits for the read and
+	 * write pointers. This technique avoids wasting a slot in the buffer.
+	 * Read and write offsets are calculated from the pointers in order to
+	 * check if the write pointer has wrapped around the array.
+	 */
+	xecore_buf = &stream->xecore_buf[xecore];
+	xecore_start_vaddr = xecore_buf->vaddr;
+	read_ptr = xecore_buf->read;
+	write_ptr = xecore_buf->write;
+	buf_size = stream->per_xecore_buf_size;
+
+	read_data_size = buf_data_size(buf_size, read_ptr, write_ptr);
+	/* Read only the data that the user space buffer can accommodate */
+	read_data_size = min_t(size_t, count - *total_data_size, read_data_size);
+	if (read_data_size == 0)
+		return 0;
+
+	read_offset = read_ptr & (buf_size - 1);
+	write_offset = write_ptr & (buf_size - 1);
+	read_vaddr = xecore_start_vaddr + read_offset;
+
+	if (write_offset > read_offset) {
+		if (copy_to_user(buf + *total_data_size, read_vaddr, read_data_size))
+			return -EFAULT;
+	} else {
+		if (read_data_size >= buf_size - read_offset)
+			copy_size = buf_size - read_offset;
+		else
+			copy_size = read_data_size;
+		if (copy_to_user(buf + *total_data_size, read_vaddr, copy_size))
+			return -EFAULT;
+		if (copy_to_user(buf + *total_data_size + copy_size,
+				 xecore_start_vaddr, read_data_size - copy_size))
+			return -EFAULT;
+	}
+
+	*total_data_size += read_data_size;
+	read_ptr += read_data_size;
+
+	/* Read pointer can overflow into one additional bit */
+	read_ptr &= (buf_size << 1) - 1;
+	read_ptr_reg = REG_FIELD_PREP(XEHPC_EUSTALL_REPORT1_READ_PTR_MASK, (read_ptr >> 6));
+	read_ptr_reg = _MASKED_FIELD(XEHPC_EUSTALL_REPORT1_READ_PTR_MASK, read_ptr_reg);
+	xe_gt_mcr_unicast_write(gt, XEHPC_EUSTALL_REPORT1, read_ptr_reg, group, instance);
+	xecore_buf->read = read_ptr;
+	trace_xe_eu_stall_data_read(group, instance, read_ptr, write_ptr,
+				    read_data_size, *total_data_size);
+	return 0;
+}
+
+/**
+ * xe_eu_stall_stream_read_locked - copy EU stall counters data from the
+ *				    per xecore buffers to the userspace buffer
+ * @stream: A stream opened for EU stall count metrics
+ * @file: An xe EU stall data stream file
+ * @buf: destination buffer given by userspace
+ * @count: the number of bytes userspace wants to read
+ *
+ * Returns: Number of bytes copied or a negative error code
+ * If we've successfully copied any data then reporting that takes
+ * precedence over any internal error status, so the data isn't lost.
+ */
+static ssize_t xe_eu_stall_stream_read_locked(struct xe_eu_stall_data_stream *stream,
+					      struct file *file, char __user *buf,
+					      size_t count)
+{
+	struct xe_gt *gt = stream->gt;
+	size_t total_size = 0;
+	u16 group, instance;
+	unsigned int xecore;
+	int ret = 0;
+
+	for_each_dss_steering(xecore, gt, group, instance) {
+		ret = xe_eu_stall_data_buf_read(stream, buf, count, &total_size,
+						gt, group, instance, xecore);
+		if (ret || count == total_size)
+			break;
+	}
+	return total_size ?: (ret ?: -EAGAIN);
+}
+
 /*
  * Userspace must enable the EU stall stream with DRM_XE_OBSERVATION_IOCTL_ENABLE
  * before calling read().
  */
 static ssize_t xe_eu_stall_stream_read(struct file *file, char __user *buf,
 				       size_t count, loff_t *ppos)
 {
-	ssize_t ret = 0;
+	struct xe_eu_stall_data_stream *stream = file->private_data;
+	struct xe_gt *gt = stream->gt;
+	ssize_t ret, aligned_count;
+
+	aligned_count = ALIGN_DOWN(count, stream->data_record_size);
+	if (aligned_count == 0)
+		return -EINVAL;
+
+	if (!stream->enabled) {
+		xe_gt_dbg(gt, "EU stall data stream not enabled to read\n");
+		return -EINVAL;
+	}
+
+	if (!(file->f_flags & O_NONBLOCK)) {
+		do {
+			ret = wait_event_interruptible(stream->poll_wq, stream->pollin);
+			if (ret)
+				return -EINTR;
+
+			mutex_lock(&gt->eu_stall->stream_lock);
+			ret = xe_eu_stall_stream_read_locked(stream, file, buf, aligned_count);
+			mutex_unlock(&gt->eu_stall->stream_lock);
+		} while (ret == -EAGAIN);
+	} else {
+		mutex_lock(&gt->eu_stall->stream_lock);
+		ret = xe_eu_stall_stream_read_locked(stream, file, buf, aligned_count);
+		mutex_unlock(&gt->eu_stall->stream_lock);
+	}
+
+	/*
+	 * This may not work correctly if the user buffer is very small.
+	 * We don't want to block the next read() when there is data in the buffer
+	 * now, but couldn't be accommodated in the small user buffer.
+	 */
+	stream->pollin = false;
 
 	return ret;
 }
@@ -348,6 +565,21 @@ static int xe_eu_stall_stream_enable(struct xe_eu_stall_data_stream *stream)
 	return 0;
 }
 
+static void eu_stall_data_buf_poll_work_fn(struct work_struct *work)
+{
+	struct xe_eu_stall_data_stream *stream =
+		container_of(work, typeof(*stream), buf_poll_work.work);
+	struct xe_gt *gt = stream->gt;
+
+	if (eu_stall_data_buf_poll(stream)) {
+		stream->pollin = true;
+		wake_up(&stream->poll_wq);
+	}
+	queue_delayed_work(gt->eu_stall->buf_ptr_poll_wq,
+			   &stream->buf_poll_work,
+			   msecs_to_jiffies(POLL_PERIOD_MS));
+}
+
 static int xe_eu_stall_stream_init(struct xe_eu_stall_data_stream *stream,
 				   struct eu_stall_open_properties *props)
 {
@@ -372,6 +604,9 @@ static int xe_eu_stall_stream_init(struct xe_eu_stall_data_stream *stream,
 			  max_wait_num_reports);
 		return -EINVAL;
 	}
+
+	init_waitqueue_head(&stream->poll_wq);
+	INIT_DELAYED_WORK(&stream->buf_poll_work, eu_stall_data_buf_poll_work_fn);
 	stream->per_xecore_buf_size = per_xecore_buf_size;
 	stream->sampling_rate_mult = props->sampling_rate_mult;
 	stream->wait_num_reports = props->wait_num_reports;
@@ -389,15 +624,35 @@ static int xe_eu_stall_stream_init(struct xe_eu_stall_data_stream *stream,
 	return 0;
 }
 
+static __poll_t xe_eu_stall_stream_poll_locked(struct xe_eu_stall_data_stream *stream,
+					       struct file *file, poll_table *wait)
+{
+	__poll_t events = 0;
+
+	poll_wait(file, &stream->poll_wq, wait);
+
+	if (stream->pollin)
+		events |= EPOLLIN;
+
+	return events;
+}
+
 static __poll_t xe_eu_stall_stream_poll(struct file *file, poll_table *wait)
 {
-	__poll_t ret = 0;
+	struct xe_eu_stall_data_stream *stream = file->private_data;
+	struct xe_gt *gt = stream->gt;
+	__poll_t ret;
+
+	mutex_lock(&gt->eu_stall->stream_lock);
+	ret = xe_eu_stall_stream_poll_locked(stream, file, wait);
+	mutex_unlock(&gt->eu_stall->stream_lock);
 
 	return ret;
 }
 
 static int xe_eu_stall_enable_locked(struct xe_eu_stall_data_stream *stream)
 {
+	struct xe_gt *gt = stream->gt;
 	int ret = 0;
 
 	if (stream->enabled)
@@ -406,6 +661,10 @@ static int xe_eu_stall_enable_locked(struct xe_eu_stall_data_stream *stream)
 	stream->enabled = true;
 
 	ret = xe_eu_stall_stream_enable(stream);
+
+	queue_delayed_work(gt->eu_stall->buf_ptr_poll_wq,
+			   &stream->buf_poll_work,
+			   msecs_to_jiffies(POLL_PERIOD_MS));
 	return ret;
 }
 
@@ -420,6 +679,8 @@ static int xe_eu_stall_disable_locked(struct xe_eu_stall_data_stream *stream)
 
 	xe_gt_mcr_multicast_write(gt, XEHPC_EUSTALL_BASE, 0);
 
+	cancel_delayed_work_sync(&stream->buf_poll_work);
+
 	xe_force_wake_put(gt_to_fw(gt), XE_FW_RENDER);
 	xe_pm_runtime_put(gt_to_xe(gt));