[PATCH 18/19] nitro_enclaves: Time the wait for the device to turn off by the clock

[Alexander Graf <graf@amazon.com>]

Unbind, shutdown and the next probe give the nitro_enclaves device
NE_DEFAULT_TIMEOUT_MSECS, 120 s, to turn off. The device turns off only
once it has stopped every enclave and scrubbed its memory, which can
take as long as a single ENCLAVE_STOP. ne_pci_dev_disable() also counts
the wait in 10 ms steps of msleep_interruptible(). At HZ=100 each step
sleeps two jiffies, so the wait takes 240 s, and with a signal pending
it does not sleep at all.

Allow the device NE_FREE_TIMEOUT_MSECS, 10 minutes, as for ENCLAVE_STOP,
and poll the register with readx_poll_timeout(), which keeps a ktime
deadline.

Kiro, an AI coding assistant, found this while timing an unbind on
hardware.

Fixes: 89308c11ae3b ("nitro_enclaves: Init PCI device driver")
Signed-off-by: Alexander Graf <graf@amazon.com>
---
 drivers/virt/nitro_enclaves/ne_pci_dev.c | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/drivers/virt/nitro_enclaves/ne_pci_dev.c b/drivers/virt/nitro_enclaves/ne_pci_dev.c
index cd8e934e968c3..edc72d4f623e5 100644
--- a/drivers/virt/nitro_enclaves/ne_pci_dev.c
+++ b/drivers/virt/nitro_enclaves/ne_pci_dev.c
@@ -9,6 +9,7 @@
 
 #include <linux/delay.h>
 #include <linux/device.h>
+#include <linux/iopoll.h>
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
@@ -550,8 +551,7 @@ static void ne_pci_dev_disable(struct pci_dev *pdev)
 {
 	u8 dev_disable_reply = 0;
 	struct ne_pci_dev *ne_pci_dev = pci_get_drvdata(pdev);
-	const unsigned int sleep_time = 10; /* 10 ms */
-	unsigned int sleep_time_count = 0;
+	int rc;
 
 	iowrite8(NE_ENABLE_OFF, ne_pci_dev->iomem_base + NE_ENABLE);
 
@@ -560,17 +560,12 @@ static void ne_pci_dev_disable(struct pci_dev *pdev)
 	 * state is not immediately set to disabled and going through a
 	 * transitory state of disabling.
 	 */
-	while (sleep_time_count < NE_DEFAULT_TIMEOUT_MSECS) {
-		dev_disable_reply = ioread8(ne_pci_dev->iomem_base + NE_ENABLE);
-		if (dev_disable_reply == NE_ENABLE_OFF)
-			return;
-
-		msleep_interruptible(sleep_time);
-		sleep_time_count += sleep_time;
-	}
-
-	dev_disable_reply = ioread8(ne_pci_dev->iomem_base + NE_ENABLE);
-	if (dev_disable_reply != NE_ENABLE_OFF)
+	rc = readx_poll_timeout(ioread8, ne_pci_dev->iomem_base + NE_ENABLE,
+				dev_disable_reply,
+				dev_disable_reply == NE_ENABLE_OFF,
+				10 * USEC_PER_MSEC,
+				NE_FREE_TIMEOUT_MSECS * USEC_PER_MSEC);
+	if (rc < 0)
 		dev_err(&pdev->dev, "Error in pci dev disable cmd\n");
 }
 
-- 
2.47.1