[PATCH v2] lspci: Show Slot Power Limit values above EFh

["Pali Rohár" <pali@kernel.org>]

PCI Express Base Specification rev. 3.0 has the following definition for
the Slot Power Limit Value:

=======================================================================
When the Slot Power Limit Scale field equals 00b (1.0x) and Slot Power
Limit Value exceeds EFh, the following alternative encodings are used:
  F0h = 250 W Slot Power Limit
  F1h = 275 W Slot Power Limit
  F2h = 300 W Slot Power Limit
  F3h to FFh = Reserved for Slot Power Limit values above 300 W
=======================================================================

Replace function power_limit() by show_power_limit() which also prints
power limit value. Show reserved value as string ">300W" and omit usage of
floating point variables as it is not needed.
---
 ls-caps.c | 38 ++++++++++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 10 deletions(-)

diff --git a/ls-caps.c b/ls-caps.c
index db56556971cb..7fa6c1da45bd 100644
--- a/ls-caps.c
+++ b/ls-caps.c
@@ -656,10 +656,27 @@ static int exp_downstream_port(int type)
 	 type == PCI_EXP_TYPE_PCIE_BRIDGE;	/* PCI/PCI-X to PCIe Bridge */
 }
 
-static float power_limit(int value, int scale)
+static void show_power_limit(int value, int scale)
 {
-  static const float scales[4] = { 1.0, 0.1, 0.01, 0.001 };
-  return value * scales[scale];
+  static const int scales[4] = { 1000, 100, 10, 1 };
+  static const int scale0_values[3] = { 250, 275, 300 };
+  if (scale == 0 && value >= 0xF0) {
+    /* F3h to FFh = Reserved for Slot Power Limit values above 300 W */
+    if (value >= 0xF3) {
+      printf(">300W");
+      return;
+    }
+    value = scale0_values[value - 0xF0];
+  }
+  value *= scales[scale];
+  printf("%d", value / 1000);
+  if (value % 10)
+    printf(".%03d", value % 1000);
+  else if (value % 100)
+    printf(".%02d", (value / 10) % 100);
+  else if (value % 1000)
+    printf(".%d", (value / 100) % 10);
+  printf("W");
 }
 
 static const char *latency_l0s(int value)
@@ -700,10 +717,10 @@ static void cap_express_dev(struct device *d, int where, int type)
     printf(" FLReset%c",
 	FLAG(t, PCI_EXP_DEVCAP_FLRESET));
   if ((type == PCI_EXP_TYPE_ENDPOINT) || (type == PCI_EXP_TYPE_UPSTREAM) ||
-      (type == PCI_EXP_TYPE_PCI_BRIDGE))
-    printf(" SlotPowerLimit %.3fW",
-	power_limit((t & PCI_EXP_DEVCAP_PWR_VAL) >> 18,
-		    (t & PCI_EXP_DEVCAP_PWR_SCL) >> 26));
+      (type == PCI_EXP_TYPE_PCI_BRIDGE)) {
+    printf(" SlotPowerLimit ");
+    show_power_limit((t & PCI_EXP_DEVCAP_PWR_VAL) >> 18, (t & PCI_EXP_DEVCAP_PWR_SCL) >> 26);
+  }
   printf("\n");
 
   w = get_conf_word(d, where + PCI_EXP_DEVCTL);
@@ -871,9 +888,10 @@ static void cap_express_slot(struct device *d, int where)
 	FLAG(t, PCI_EXP_SLTCAP_PWRI),
 	FLAG(t, PCI_EXP_SLTCAP_HPC),
 	FLAG(t, PCI_EXP_SLTCAP_HPS));
-  printf("\t\t\tSlot #%d, PowerLimit %.3fW; Interlock%c NoCompl%c\n",
-	(t & PCI_EXP_SLTCAP_PSN) >> 19,
-	power_limit((t & PCI_EXP_SLTCAP_PWR_VAL) >> 7, (t & PCI_EXP_SLTCAP_PWR_SCL) >> 15),
+  printf("\t\t\tSlot #%d, PowerLimit ",
+	(t & PCI_EXP_SLTCAP_PSN) >> 19);
+  show_power_limit((t & PCI_EXP_SLTCAP_PWR_VAL) >> 7, (t & PCI_EXP_SLTCAP_PWR_SCL) >> 15);
+  printf("; Interlock%c NoCompl%c\n",
 	FLAG(t, PCI_EXP_SLTCAP_INTERLOCK),
 	FLAG(t, PCI_EXP_SLTCAP_NOCMDCOMP));
 
-- 
2.20.1