[PATCH] wifi: ath12k: fix CMA error and MHI state mismatch during resume

[Saikiran <bjsaikiran@gmail.com>]

Commit 8d5f4da8d70b ("wifi: ath12k: support suspend/resume") introduced
system suspend/resume support but caused a critical regression where
CMA pages are corrupted during resume.

1. CMA page corruption:
   Calling mhi_unprepare_after_power_down() during suspend (via
   ATH12K_MHI_DEINIT) prematurely frees the fbc_image and rddm_image
   DMA buffers. When these pages are accessed during resume, the kernel
   detects corruption (Bad page state).

To fix this corruption, the driver must skip ATH12K_MHI_DEINIT during
suspend, preserving the DMA buffers. However, implementing this fix
exposes a second issue in the state machine:

2. Resume failure due to MHI state mismatch:
   When DEINIT is skipped during suspend to protect the memory, the
   ATH12K_MHI_INIT bit remains set. On resume, ath12k_mhi_start()
   blindly attempts to set INIT again, but the state machine rejects
   the transition:

   ath12k_wifi7_pci ...: failed to set mhi state INIT(0) in current
   mhi state (0x1)

Fix the corruption and enable the correct suspend flow by:

1. In ath12k_mhi_stop(), skipping ATH12K_MHI_DEINIT if suspending.
   This prevents the memory corruption by keeping the device context
   valid (MHI_POWER_OFF_KEEP_DEV).

2. In ath12k_mhi_start(), checking if MHI_INIT is already set.
   This accommodates the new suspend flow where the device remains
   initialized, allowing the driver to proceed directly to POWER_ON.

Tested with suspend/resume cycles on Qualcomm Snapdragon X Elite
(SC8380XP) with WCN7850 WiFi. No CMA corruption observed, WiFi resumes
successfully, and deep sleep works correctly.

Fixes: 8d5f4da8d70b ("wifi: ath12k: support suspend/resume")
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c5-00302 (Lenovo Yoga Slim 7x)
Signed-off-by: Saikiran <bjsaikiran@gmail.com>
---
 drivers/net/wireless/ath/ath12k/mhi.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireless/ath/ath12k/mhi.c b/drivers/net/wireless/ath/ath12k/mhi.c
index 45c0f66dcc5e..1a0b3bcc6bbf 100644
--- a/drivers/net/wireless/ath/ath12k/mhi.c
+++ b/drivers/net/wireless/ath/ath12k/mhi.c
@@ -485,9 +485,14 @@ int ath12k_mhi_start(struct ath12k_pci *ab_pci)
 
 	ab_pci->mhi_ctrl->timeout_ms = MHI_TIMEOUT_DEFAULT_MS;
 
-	ret = ath12k_mhi_set_state(ab_pci, ATH12K_MHI_INIT);
-	if (ret)
-		goto out;
+	/* In case of suspend/resume, MHI INIT is already done.
+	 * So check if MHI INIT is set or not.
+	 */
+	if (!test_bit(ATH12K_MHI_INIT, &ab_pci->mhi_state)) {
+		ret = ath12k_mhi_set_state(ab_pci, ATH12K_MHI_INIT);
+		if (ret)
+			goto out;
+	}
 
 	ret = ath12k_mhi_set_state(ab_pci, ATH12K_MHI_POWER_ON);
 	if (ret)
@@ -501,16 +506,21 @@ int ath12k_mhi_start(struct ath12k_pci *ab_pci)
 
 void ath12k_mhi_stop(struct ath12k_pci *ab_pci, bool is_suspend)
 {
-	/* During suspend we need to use mhi_power_down_keep_dev()
-	 * workaround, otherwise ath12k_core_resume() will timeout
-	 * during resume.
+	/* During suspend, we need to use mhi_power_down_keep_dev()
+	 * and avoid calling MHI_DEINIT. The deinit frees BHIE tables
+	 * which causes memory corruption when those pages are
+	 * accessed/freed again during resume. We want to keep the
+	 * device prepared for resume, otherwise ath12k_core_resume()
+	 * will timeout.
 	 */
 	if (is_suspend)
 		ath12k_mhi_set_state(ab_pci, ATH12K_MHI_POWER_OFF_KEEP_DEV);
 	else
 		ath12k_mhi_set_state(ab_pci, ATH12K_MHI_POWER_OFF);
 
-	ath12k_mhi_set_state(ab_pci, ATH12K_MHI_DEINIT);
+	/* Only deinit when doing full power down, not during suspend */
+	if (!is_suspend)
+		ath12k_mhi_set_state(ab_pci, ATH12K_MHI_DEINIT);
 }
 
 void ath12k_mhi_suspend(struct ath12k_pci *ab_pci)
-- 
2.51.0