linux-kernel - [PATCH AUTOSEL 6.17-6.12] scsi: ufs: host: mediatek: Correct system PM flow

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Message-ID: <20251025160905.3857885-444-sashal@kernel.org>
Date: Sat, 25 Oct 2025 12:01:15 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Peter Wang <peter.wang@...iatek.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Sasha Levin <sashal@...nel.org>,
	matthias.bgg@...il.com,
	angelogioacchino.delregno@...labora.com,
	linux-scsi@...r.kernel.org,
	linux-mediatek@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: [PATCH AUTOSEL 6.17-6.12] scsi: ufs: host: mediatek: Correct system PM flow

From: Peter Wang <peter.wang@...iatek.com>

[ Upstream commit 77b96ef70b6ba46e3473e5e3a66095c4bc0e93a4 ]

Refine the system power management (PM) flow by skipping low power mode
(LPM) and MTCMOS settings if runtime PM is already applied. Prevent
redundant operations to ensure a more efficient PM process.

Signed-off-by: Peter Wang <peter.wang@...iatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---

LLM Generated explanations, may be completely bogus:

YES

- Fixes a real PM logic bug. Without this change, the Mediatek UFS
  driver forces VSx/regulators out of LPM and re-enables MTCMOS during
  system resume even if the device is runtime-suspended, which violates
  the runtime PM state and can wake hardware spuriously (extra power
  draw or mis-ordered bring-up). The core UFS system PM paths already
  skip work if the device is runtime-suspended; the Mediatek vendor code
  must mirror that behavior.
- Aligns vendor flow with core UFS PM semantics. Core checks
  `pm_runtime_suspended(hba->dev)` and bails from system PM work in both
  suspend and resume (drivers/ufs/core/ufshcd.c:10284,
  drivers/ufs/core/ufshcd.c:10311). This patch adds the same guards to
  the Mediatek hooks so vendor-specific toggles are not performed on a
  runtime-suspended device.
- Corrects ordering on resume. It powers the MTCMOS domain before
  changing device regulator LPM, matching the already-correct runtime PM
  path and avoiding SMC/PM operations while the domain is off.

Key code changes and impact:
- Add guard in system suspend to skip vendor LPM/MTCMOS when runtime-
  suspended:
  - `if (pm_runtime_suspended(hba->dev)) goto out;`
    drivers/ufs/host/ufs-mediatek.c:2380
  - Prevents redundant `ufs_mtk_dev_vreg_set_lpm(hba, true)` and
    `ufs_mtk_mtcmos_ctrl(false, ...)` calls when runtime PM already put
    the device in low power (drivers/ufs/host/ufs-mediatek.c:2383,
    drivers/ufs/host/ufs-mediatek.c:2386).
- Add guard in system resume to preserve runtime-suspended state:
  - `if (pm_runtime_suspended(hba->dev)) goto out;`
    drivers/ufs/host/ufs-mediatek.c:2398
  - Avoids powering on MTCMOS and clearing LPM when device should remain
    runtime-suspended.
- Fix resume sequencing to match runtime resume:
  - Enable MTCMOS before clearing LPM: `ufs_mtk_mtcmos_ctrl(true, ...)`
    then `ufs_mtk_dev_vreg_set_lpm(hba, false)` (drivers/ufs/host/ufs-
    mediatek.c:2401, drivers/ufs/host/ufs-mediatek.c:2404).
  - Mirrors the runtime path order (drivers/ufs/host/ufs-
    mediatek.c:2442, drivers/ufs/host/ufs-mediatek.c:2448).
- Always invoke core system resume for tracing/consistency
  (drivers/ufs/host/ufs-mediatek.c:2406).

Why it fits stable:
- Small, contained fix limited to Mediatek UFS host.
- No API changes; just conditionalizing existing operations and
  correcting order.
- Prevents incorrect power-state transitions and redundant SMC/PM ops;
  low regression risk.
- Aligns with core driver’s established PM behavior, reducing divergence
  and surprises.

Given these factors, this is an important behavioral fix with minimal
risk and should be backported.

 drivers/ufs/host/ufs-mediatek.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/ufs/host/ufs-mediatek.c b/drivers/ufs/host/ufs-mediatek.c
index 6bdbbee1f0708..91081d2aabe44 100644
--- a/drivers/ufs/host/ufs-mediatek.c
+++ b/drivers/ufs/host/ufs-mediatek.c
@@ -2264,27 +2264,38 @@ static int ufs_mtk_system_suspend(struct device *dev)
 
 	ret = ufshcd_system_suspend(dev);
 	if (ret)
-		return ret;
+		goto out;
+
+	if (pm_runtime_suspended(hba->dev))
+		goto out;
 
 	ufs_mtk_dev_vreg_set_lpm(hba, true);
 
 	if (ufs_mtk_is_rtff_mtcmos(hba))
 		ufs_mtk_mtcmos_ctrl(false, res);
 
-	return 0;
+out:
+	return ret;
 }
 
 static int ufs_mtk_system_resume(struct device *dev)
 {
+	int ret = 0;
 	struct ufs_hba *hba = dev_get_drvdata(dev);
 	struct arm_smccc_res res;
 
+	if (pm_runtime_suspended(hba->dev))
+		goto out;
+
 	ufs_mtk_dev_vreg_set_lpm(hba, false);
 
 	if (ufs_mtk_is_rtff_mtcmos(hba))
 		ufs_mtk_mtcmos_ctrl(true, res);
 
-	return ufshcd_system_resume(dev);
+out:
+	ret = ufshcd_system_resume(dev);
+
+	return ret;
 }
 #endif
 
-- 
2.51.0