e1000e: Fix the max snoop/no-snoop latency for 10M

We should decode the latency and the max_latency before directly compare.
The latency should be presented as lat_enc = scale x value:
lat_enc_d = (lat_enc & 0x0x3ff) x (1U << (5*((max_ltr_enc & 0x1c00)
>> 10)))

Fixes: cf8fb73 ("e1000e: add support for LTR on I217/I218")
Suggested-by: Yee Li <seven.yi.lee@gmail.com>
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Author: Sasha Neftin

drivers/net/ethernet/intel/e1000e/ich8lan.c

@@ -1006,6 +1006,8 @@ static s32 e1000_platform_pm_pch_lpt(struct e1000_hw *hw, bool link)
 {
 	u32 reg = link << (E1000_LTRV_REQ_SHIFT + E1000_LTRV_NOSNOOP_SHIFT) |
 	    link << E1000_LTRV_REQ_SHIFT | E1000_LTRV_SEND;
+	u16 max_ltr_enc_d = 0;	/* maximum LTR decoded by platform */
+	u16 lat_enc_d = 0;	/* latency decoded */
 	u16 lat_enc = 0;	/* latency encoded */
 
 	if (link) {
@@ -1059,7 +1061,17 @@ static s32 e1000_platform_pm_pch_lpt(struct e1000_hw *hw, bool link)
 				     E1000_PCI_LTR_CAP_LPT + 2, &max_nosnoop);
 		max_ltr_enc = max_t(u16, max_snoop, max_nosnoop);
 
-		if (lat_enc > max_ltr_enc)
+		lat_enc_d = (lat_enc & E1000_LTRV_VALUE_MASK) *
+			     (1U << (E1000_LTRV_SCALE_FACTOR *
+			     ((lat_enc & E1000_LTRV_SCALE_MASK)
+			     >> E1000_LTRV_SCALE_SHIFT)));
+
+		max_ltr_enc_d = (max_ltr_enc & E1000_LTRV_VALUE_MASK) *
+				 (1U << (E1000_LTRV_SCALE_FACTOR *
+				 ((max_ltr_enc & E1000_LTRV_SCALE_MASK)
+				 >> E1000_LTRV_SCALE_SHIFT)));
+
+		if (lat_enc_d > max_ltr_enc_d)
 			lat_enc = max_ltr_enc;
 	}
 

drivers/net/ethernet/intel/e1000e/ich8lan.h

@@ -274,8 +274,11 @@
 
 /* Latency Tolerance Reporting */
 #define E1000_LTRV			0x000F8
+#define E1000_LTRV_VALUE_MASK		0x000003FF
 #define E1000_LTRV_SCALE_MAX		5
 #define E1000_LTRV_SCALE_FACTOR		5
+#define E1000_LTRV_SCALE_SHIFT		10
+#define E1000_LTRV_SCALE_MASK		0x00001C00
 #define E1000_LTRV_REQ_SHIFT		15
 #define E1000_LTRV_NOSNOOP_SHIFT	16
 #define E1000_LTRV_SEND			(1 << 30)