[PATCH v8 4/7] drm/xe/eustall: Return -EIO error from read() if HW drops data

[Harish Chegondi]

If the user space doesn't read the EU stall data fast enough,
it is possible that the EU stall data buffer can get filled,
and if the hardware wants to write more data, it simply drops
data due to unavailable buffer space. In that case, hardware
sets a bit in a register. If the driver detects data drop,
the driver read() returns -EIO error to let the user space
know that HW has dropped data. The -EIO error is returned
even if there is EU stall data in the buffer. A subsequent
read by the user space returns the remaining EU stall data.

Signed-off-by: Harish Chegondi <harish.chegondi at intel.com>
---
 drivers/gpu/drm/xe/xe_eu_stall.c | 12 ++++++++++++
 drivers/gpu/drm/xe/xe_eu_stall.h |  1 +
 2 files changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_eu_stall.c b/drivers/gpu/drm/xe/xe_eu_stall.c
index c388d733b857..437782f8433c 100644
--- a/drivers/gpu/drm/xe/xe_eu_stall.c
+++ b/drivers/gpu/drm/xe/xe_eu_stall.c
@@ -472,6 +472,7 @@ xe_eu_stall_stream_read_locked(struct xe_eu_stall_data_stream *stream,
  * before calling read().
  *
  * Returns: The number of bytes copied or a negative error code on failure.
+ *	    -EIO if HW drops any EU stall data when the buffer is full.
  */
 static ssize_t xe_eu_stall_stream_read(struct file *file, char __user *buf,
 				       size_t count, loff_t *ppos)
@@ -485,6 +486,16 @@ static ssize_t xe_eu_stall_stream_read(struct file *file, char __user *buf,
 		return -EINVAL;
 	}
 
+	if (bitmap_weight(stream->data_drop.mask, XE_MAX_DSS_FUSE_BITS)) {
+		if (!stream->data_drop.reported_to_user) {
+			stream->data_drop.reported_to_user = true;
+			xe_gt_dbg(gt, "EU stall data dropped in XeCores: %*pb\n",
+				  XE_MAX_DSS_FUSE_BITS, stream->data_drop.mask);
+			return -EIO;
+		}
+		stream->data_drop.reported_to_user = false;
+	}
+
 	if (!(file->f_flags & O_NONBLOCK)) {
 		do {
 			if (!stream->pollin) {
@@ -680,6 +691,7 @@ static int xe_eu_stall_stream_init(struct xe_eu_stall_data_stream *stream,
 	if (!stream->xecore_buf)
 		return -ENOMEM;
 
+	stream->data_drop.reported_to_user = false;
 	bitmap_zero(stream->data_drop.mask, XE_MAX_DSS_FUSE_BITS);
 
 	xe_pm_runtime_get(gt_to_xe(gt));
diff --git a/drivers/gpu/drm/xe/xe_eu_stall.h b/drivers/gpu/drm/xe/xe_eu_stall.h
index f97c8bf8e852..8bc44e9e98af 100644
--- a/drivers/gpu/drm/xe/xe_eu_stall.h
+++ b/drivers/gpu/drm/xe/xe_eu_stall.h
@@ -31,6 +31,7 @@ struct xe_eu_stall_data_stream {
 	struct xe_bo *bo;
 	struct per_xecore_buf *xecore_buf;
 	struct {
+		bool reported_to_user;
 		xe_dss_mask_t mask;
 	} data_drop;
 	struct hrtimer poll_check_timer;
-- 
2.47.1