[PATCH RFC v1] vdpa/ifcvf: Time out and report device reset failure

[Yuho Choi <oss.patchbox@gmail.com>]

ifcvf_reset() writes 0 to device_status and polls it without a bound,
and ifcvf_vdpa_reset() always returns 0. A device that does not finish
the reset, or one that was surprise-removed and reads back 0xff, keeps
the caller in the reset path forever.

Bound the poll with readx_poll_timeout() and return -ETIMEDOUT from
.reset, so that callers such as VHOST_VDPA_SET_STATUS(0) see the failure
instead of hanging. Stop right away with -ENODEV once the device reads
back all ones and is no longer present, as there is nothing left to
wait for.

Fixes: 386a26208524 ("vDPA/ifcvf: synchronize irqs in the reset routine")
Signed-off-by: Yuho Choi <oss.patchbox@gmail.com>
---
RFC for two reasons:
- The spec gives no bound for a reset; 10 seconds follows octeon_ep's
  OCTEP_HW_TIMEOUT.
- vhost_vdpa_release() ignores a reset failure and still tears the
  mappings down, so on close a timeout turns a hang into teardown while
  the device may still be active. That needs a separate fix in
  vhost-vdpa.

Compile-tested only (x86_64 defconfig + IFCVF, W=1).

 drivers/vdpa/ifcvf/ifcvf_base.c | 24 +++++++++++++++++++++---
 drivers/vdpa/ifcvf/ifcvf_base.h |  3 ++-
 drivers/vdpa/ifcvf/ifcvf_main.c |  4 +---
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/drivers/vdpa/ifcvf/ifcvf_base.c b/drivers/vdpa/ifcvf/ifcvf_base.c
index d5507b63b6cdb..8a6c8f8314d53 100644
--- a/drivers/vdpa/ifcvf/ifcvf_base.c
+++ b/drivers/vdpa/ifcvf/ifcvf_base.c
@@ -8,6 +8,8 @@
  *
  */
 
+#include <linux/iopoll.h>
+
 #include "ifcvf_base.h"
 
 u16 ifcvf_set_vq_vector(struct ifcvf_hw *hw, u16 qid, int vector)
@@ -201,11 +203,27 @@ void ifcvf_set_status(struct ifcvf_hw *hw, u8 status)
 	vp_iowrite8(status, &hw->common_cfg->device_status);
 }
 
-void ifcvf_reset(struct ifcvf_hw *hw)
+static bool ifcvf_reset_done(struct ifcvf_hw *hw, u8 status)
 {
+	/* A surprise-removed device reads back all ones and never resets */
+	return !status || (status == 0xff && !pci_device_is_present(hw->pdev));
+}
+
+int ifcvf_reset(struct ifcvf_hw *hw)
+{
+	u8 status;
+	int ret;
+
 	ifcvf_set_status(hw, 0);
-	while (ifcvf_get_status(hw))
-		msleep(1);
+	ret = readx_poll_timeout(ifcvf_get_status, hw, status,
+				 ifcvf_reset_done(hw, status),
+				 1000, IFCVF_RESET_TIMEOUT_US);
+	if (ret) {
+		IFCVF_ERR(hw->pdev, "timed out waiting for device reset\n");
+		return ret;
+	}
+
+	return status ? -ENODEV : 0;
 }
 
 u64 ifcvf_get_hw_features(struct ifcvf_hw *hw)
diff --git a/drivers/vdpa/ifcvf/ifcvf_base.h b/drivers/vdpa/ifcvf/ifcvf_base.h
index aa36de361c10e..57d00b881582b 100644
--- a/drivers/vdpa/ifcvf/ifcvf_base.h
+++ b/drivers/vdpa/ifcvf/ifcvf_base.h
@@ -29,6 +29,7 @@
 
 #define IFCVF_LM_BAR			4
 #define IFCVF_MIN_VQ_SIZE		64
+#define IFCVF_RESET_TIMEOUT_US		(10 * USEC_PER_SEC)
 
 #define IFCVF_ERR(pdev, fmt, ...)	dev_err(&pdev->dev, fmt, ##__VA_ARGS__)
 #define IFCVF_DBG(pdev, fmt, ...)	dev_dbg(&pdev->dev, fmt, ##__VA_ARGS__)
@@ -112,7 +113,7 @@ void ifcvf_write_dev_config(struct ifcvf_hw *hw, u64 offset,
 			    const void *src, int length);
 u8 ifcvf_get_status(struct ifcvf_hw *hw);
 void ifcvf_set_status(struct ifcvf_hw *hw, u8 status);
-void ifcvf_reset(struct ifcvf_hw *hw);
+int ifcvf_reset(struct ifcvf_hw *hw);
 u64 ifcvf_get_dev_features(struct ifcvf_hw *hw);
 u64 ifcvf_get_hw_features(struct ifcvf_hw *hw);
 int ifcvf_verify_min_features(struct ifcvf_hw *hw, u64 features);
diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c b/drivers/vdpa/ifcvf/ifcvf_main.c
index 2af1cec958848..6c569f01bec91 100644
--- a/drivers/vdpa/ifcvf/ifcvf_main.c
+++ b/drivers/vdpa/ifcvf/ifcvf_main.c
@@ -444,9 +444,7 @@ static int ifcvf_vdpa_reset(struct vdpa_device *vdpa_dev)
 	if (status & VIRTIO_CONFIG_S_DRIVER_OK)
 		ifcvf_free_irq(vf);
 
-	ifcvf_reset(vf);
-
-	return 0;
+	return ifcvf_reset(vf);
 }
 
 static u16 ifcvf_vdpa_get_vq_num_max(struct vdpa_device *vdpa_dev)

base-commit: 551c722f40809618230001baccf219193e22fc5a
-- 
2.43.0