[PATCH] mfd: intel-lpss: Clamp latency tolerance to the register value mask

[raoxu <raoxu@uniontech.com>]

From: Xu Rao <raoxu@uniontech.com>

The PM QoS latency tolerance interface accepts non-negative s32 values,
but the LPSS active and idle LTR registers have only a ten-bit value
field. intel_lpss_ltr_set() selects the larger scale for requests above
1023 us and ORs val >> 5 into the register without limiting its width.

For a request of 32768 us, the shifted value is 1024 and the latency
value field becomes zero. A request of 100000 us leaves only 53 in the
value field. Still larger requests can set bits outside both the value
and scale fields. Thus a relaxed latency request can produce a much
stricter tolerance and unnecessarily restrict power saving.

Clamp the shifted value to LPSS_PRIV_LTR_VALUE_MASK before combining it
with LPSS_PRIV_LTR_SCALE_32US. This saturates oversized requests instead
of wrapping the field, matching the Intel LTR handling in sdhci-pci.
Negative values and PM_QOS_LATENCY_ANY retain their existing handling.

The supplied fix was reviewed and this commit message prepared with
OpenCode AI assistance.

Fixes: 4b45efe85263 ("mfd: Add support for Intel Sunrisepoint LPSS devices")
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Cc: stable@vger.kernel.org
---
 drivers/mfd/intel-lpss.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/mfd/intel-lpss.c b/drivers/mfd/intel-lpss.c
index 29f30ef0da99..3c3e75c23720 100644
--- a/drivers/mfd/intel-lpss.c
+++ b/drivers/mfd/intel-lpss.c
@@ -23,6 +23,7 @@
 #include <linux/io.h>
 #include <linux/ioport.h>
 #include <linux/mfd/core.h>
+#include <linux/minmax.h>
 #include <linux/module.h>
 #include <linux/pm.h>
 #include <linux/pm_qos.h>
@@ -179,7 +180,8 @@ static void intel_lpss_ltr_set(struct device *dev, s32 val)
 		ltr &= ~LPSS_PRIV_LTR_VALUE_MASK;

 		if (val > LPSS_PRIV_LTR_VALUE_MASK)
-			ltr |= LPSS_PRIV_LTR_SCALE_32US | val >> 5;
+			ltr |= LPSS_PRIV_LTR_SCALE_32US |
+			       min_t(u32, val >> 5, LPSS_PRIV_LTR_VALUE_MASK);
 		else
 			ltr |= LPSS_PRIV_LTR_SCALE_1US | val;
 	}
--
2.50.1