[PATCH AUTOSEL 6.16-6.6] phy: rockchip-pcie: Properly disable TEST_WRITE strobe signal

[Sasha Levin]

From: Geraldo Nascimento <geraldogabriel at gmail.com>

[ Upstream commit 25facbabc3fc33c794ad09d73f73268c0f8cbc7d ]

pcie_conf is used to touch TEST_WRITE strobe signal. This signal should
be enabled, a little time waited, and then disabled. Current code clearly
was copy-pasted and never disables the strobe signal. Adjust the define.
While at it, remove PHY_CFG_RD_MASK which has been unused since
64cdc0360811 ("phy: rockchip-pcie: remove unused phy_rd_cfg function").

Reviewed-by: Neil Armstrong <neil.armstrong at linaro.org>
Signed-off-by: Geraldo Nascimento <geraldogabriel at gmail.com>
Link: https://lore.kernel.org/r/d514d5d5627680caafa8b7548cbdfee4307f5440.1751322015.git.geraldogabriel@gmail.com
Signed-off-by: Vinod Koul <vkoul at kernel.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---

LLM Generated explanations, may be completely bogus:

## Backport Status: YES

This commit should be backported to stable kernel trees for the
following reasons:

### Bug Analysis
The commit fixes a clear programming bug where `PHY_CFG_WR_DISABLE` was
incorrectly defined as `1` instead of `0`. Looking at the code in
`phy_wr_cfg()` function (lines 100-120), the sequence is:
1. Write data and address to the configuration register
2. Wait 1 microsecond
3. Enable the TEST_WRITE strobe signal by writing `PHY_CFG_WR_ENABLE`
   (value 1)
4. Wait 1 microsecond
5. Intended to disable the strobe signal with `PHY_CFG_WR_DISABLE`

However, since both `PHY_CFG_WR_ENABLE` and `PHY_CFG_WR_DISABLE` were
defined as `1`, the strobe signal was never actually disabled. This
means the PHY configuration writes were leaving the strobe signal
permanently enabled, which is incorrect hardware programming.

### Impact Assessment
1. **Real bug affecting users**: This is a functional bug that affects
   all Rockchip PCIe PHY operations. The strobe signal being left
   enabled could cause:
   - Incorrect PHY configuration behavior
   - Potential power consumption issues
   - Possible hardware state corruption
   - Unpredictable PCIe link behavior

2. **Small and contained fix**: The change is minimal - just changing
   one define from `1` to `0`. This is exactly the type of targeted fix
   suitable for stable.

3. **Clear correctness**: The fix is obviously correct - a disable
   operation should use value `0`, not `1`. The bug appears to be a
   copy-paste error from the initial driver introduction in 2016 (commit
   fcffee3d54fca).

4. **Long-standing issue**: This bug has existed since the driver was
   first introduced in 2016, affecting all kernel versions with this
   driver.

5. **No architectural changes**: The fix doesn't introduce new features
   or change the driver architecture - it simply corrects an incorrect
   constant value.

6. **Low regression risk**: Changing the disable value from 1 to 0 is
   the correct behavior according to typical hardware programming
   patterns. The risk of regression is minimal since this fixes
   incorrect behavior rather than changing working functionality.

### Additional Context
The commit also removes the unused `PHY_CFG_RD_MASK` define as cleanup,
which was left over from commit 64cdc0360811. This is harmless cleanup
that doesn't affect the backport decision.

The commit message clearly describes the issue: the TEST_WRITE strobe
signal should follow a pattern of enable→wait→disable, but the current
code never actually disables it due to the incorrect define value.

This meets all the criteria for stable backports: it fixes a real bug,
is small and self-contained, has minimal risk, and corrects clearly
incorrect behavior that has been present since driver introduction.

 drivers/phy/rockchip/phy-rockchip-pcie.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/phy/rockchip/phy-rockchip-pcie.c b/drivers/phy/rockchip/phy-rockchip-pcie.c
index bd44af36c67a..63e88abc66c6 100644
--- a/drivers/phy/rockchip/phy-rockchip-pcie.c
+++ b/drivers/phy/rockchip/phy-rockchip-pcie.c
@@ -30,9 +30,8 @@
 #define PHY_CFG_ADDR_SHIFT    1
 #define PHY_CFG_DATA_MASK     0xf
 #define PHY_CFG_ADDR_MASK     0x3f
-#define PHY_CFG_RD_MASK       0x3ff
 #define PHY_CFG_WR_ENABLE     1
-#define PHY_CFG_WR_DISABLE    1
+#define PHY_CFG_WR_DISABLE    0
 #define PHY_CFG_WR_SHIFT      0
 #define PHY_CFG_WR_MASK       1
 #define PHY_CFG_PLL_LOCK      0x10
-- 
2.39.5