[PATCH AUTOSEL 5.4 19/28] mmc: rtsx_usb_sdmmc: Fix error-path in sd_set_power_mode()

[Sasha Levin <sashal@kernel.org>]

From: Ulf Hansson <ulf.hansson@linaro.org>

[ Upstream commit 47a255f7d2eabee06cfbf5b1c2379749442fd01d ]

In the error path of sd_set_power_mode() we don't update host->power_mode,
which could lead to an imbalance of the runtime PM usage count. Fix this by
always updating host->power_mode.

Reviewed-by: Avri Altman <avri.altman@sandisk.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Ricky Wu <ricky_wu@realtek.com>
Link: https://lore.kernel.org/r/20250610111633.504366-2-ulf.hansson@linaro.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

**YES**

This commit should be backported to stable kernel trees. Here's my
extensive analysis:

## Bug Analysis

The commit fixes a **runtime PM reference counting bug** in the
`sd_set_power_mode()` function. The issue is in the error handling path:

### Original Code Problem:
```c
if (power_mode == MMC_POWER_OFF) {
    err = sd_power_off(host);
    pm_runtime_put_noidle(sdmmc_dev(host));
} else {
    pm_runtime_get_noresume(sdmmc_dev(host));
    err = sd_power_on(host);
}

if (!err)
    host->power_mode = power_mode;  // Only updated on success
```

### The Bug:
1. When transitioning to `MMC_POWER_OFF`, the code calls
   `pm_runtime_put_noidle()` **regardless** of whether `sd_power_off()`
   succeeded
2. When transitioning to `MMC_POWER_ON`, the code calls
   `pm_runtime_get_noresume()` **before** calling `sd_power_on()`
3. However, `host->power_mode` is only updated if there's no error

This creates a **runtime PM reference count imbalance** because:
- If `sd_power_off()` fails, the runtime PM reference is still
  decremented, but `host->power_mode` remains at its previous value
  (likely `MMC_POWER_ON`)
- If `sd_power_on()` fails, the runtime PM reference is still
  incremented, but `host->power_mode` remains at its previous value
  (likely `MMC_POWER_OFF`)
- The early return check `if (power_mode == host->power_mode)` at the
  beginning of the function will prevent future attempts to fix the
  power state, leaving the runtime PM count permanently imbalanced

## Why This Is Suitable for Stable:

1. **Fixes a real bug**: Runtime PM reference count imbalances can lead
   to:
   - Device staying powered when it should be suspended
   - Device being suspended when it should be active
   - Power management failures
   - Potential system hangs or crashes

2. **Minimal change**: The fix is a simple one-liner that always updates
   `host->power_mode` regardless of error status

3. **Low regression risk**:
   - The change doesn't introduce new functionality
   - It doesn't alter the control flow
   - It simply ensures state consistency

4. **Clear bug fix**: This is not a feature addition or optimization -
   it's fixing incorrect error handling that violates runtime PM rules

5. **Affects users**: This bug can manifest in real-world scenarios when
   SD card power operations fail, particularly with flaky hardware or
   during system stress

6. **Subsystem contained**: The fix is limited to a single MMC host
   driver and doesn't affect core kernel infrastructure

The commit follows stable kernel rules by being a minimal, targeted fix
for a real bug that can affect system stability and power management.

 drivers/mmc/host/rtsx_usb_sdmmc.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/mmc/host/rtsx_usb_sdmmc.c b/drivers/mmc/host/rtsx_usb_sdmmc.c
index 3261560bede4..581bec5c4caf 100644
--- a/drivers/mmc/host/rtsx_usb_sdmmc.c
+++ b/drivers/mmc/host/rtsx_usb_sdmmc.c
@@ -1038,9 +1038,7 @@ static int sd_set_power_mode(struct rtsx_usb_sdmmc *host,
 		err = sd_power_on(host);
 	}
 
-	if (!err)
-		host->power_mode = power_mode;
-
+	host->power_mode = power_mode;
 	return err;
 }
 
-- 
2.39.5