fm10k/base: document ITR scale workaround

[dpdk.git] / drivers / net / fm10k / base / fm10k_type.h

diff --git a/drivers/net/fm10k/base/fm10k_type.h b/drivers/net/fm10k/base/fm10k_type.h
index df1d276..4ec18fb 100644 (file)
--- a/drivers/net/fm10k/base/fm10k_type.h
+++ b/drivers/net/fm10k/base/fm10k_type.h
@@ -350,11 +350,20 @@ struct fm10k_hw;
 #define FM10K_TDBAL(_n)                ((0x40 * (_n)) + 0x8000)
 #define FM10K_TDBAH(_n)                ((0x40 * (_n)) + 0x8001)
 #define FM10K_TDLEN(_n)                ((0x40 * (_n)) + 0x8002)
+/* When fist initialized, VFs need to know the Interrupt Throttle Rate (ITR)
+ * scale which is based on the PCIe speed but the speed information in the PCI
+ * configuration space may not be accurate. The PF already knows the ITR scale
+ * but there is no defined method to pass that information from the PF to the
+ * VF. This is accomplished during VF initialization by temporarily co-opting
+ * the yet-to-be-used TDLEN register to have the PF store the ITR shift for
+ * the VF to retrieve before the VF needs to use the TDLEN register for its
+ * intended purpose, i.e. before the Tx resources are allocated.
+ */
 #define FM10K_TDLEN_ITR_SCALE_SHIFT            9
 #define FM10K_TDLEN_ITR_SCALE_MASK             0x00000E00
-#define FM10K_TDLEN_ITR_SCALE_GEN1             4
-#define FM10K_TDLEN_ITR_SCALE_GEN2             2
-#define FM10K_TDLEN_ITR_SCALE_GEN3             1
+#define FM10K_TDLEN_ITR_SCALE_GEN1             2
+#define FM10K_TDLEN_ITR_SCALE_GEN2             1
+#define FM10K_TDLEN_ITR_SCALE_GEN3             0
 #define FM10K_TPH_TXCTRL(_n)   ((0x40 * (_n)) + 0x8003)
 #define FM10K_TPH_TXCTRL_DESC_TPHEN            0x00000020
 #define FM10K_TPH_TXCTRL_DESC_RROEN            0x00000200