I only learning the ropes, and might have missed the memo on the use of enums so forgive me. I have looked at https://www.kernel.org/doc/html/v4.10/process/coding-style.html#macros-enums... but that didn't answer my question. I'm doing a clean up of staging:rtl8192u: clearing out checkpatch errors and triming out data structures which aren't used in the code. So I came across a typedef of an enumerated type in the file: drivers/staging/rtl8192u/r8192U.h typedef enum rf_optype { RF_OP_By_SW_3wire = 0, RF_OP_By_FW, RF_OP_MAX } rf_op_type; A quick grep for this type in drivers/staging/rtl8192u directory shows that the type is never used outside that header definition. So I can remove it? Well no you can't because the values defined in the enum are used. In drivers/staging/rtl8192u/r8192U_core.c for example: priv->Rf_Mode = RF_OP_By_SW_3wire; that element priv->Rf_Mode is defined in the structure typedef struct r8192_priv { ... u8 Rf_Mode; /* For Firmware RF -R/W switch */ ... } So now to the question, as I understand it the compiler will use an int type for the enumerated type. The data structure r8192_priv doesn't use this int type because the programmer knows that a u8 will do to hold the 3 possible values defined by the enumerated type. So you're saving a few bytes in a data structure, which I'm happy about, but the point of enumerated types is, as I understand it, so that the compiler can do some checking to ensure a value is not assigned in error. Since the enum isn't being used, there is no compiler type checking, so why use an enumerated type? Might as well have used three #define values. The obvious thing to do is leave well enough alone. But I had to ask what is the correct implementation? Use the enum in the data structure, instead of u8? Or just #define a few constants? #define RF_OP_By_SW_3wire 1 #define RF_OP_By_FW 2 #define RF_OP_MAX 3 Given the space saving of u8 over int I'd probably go with the #define. Guess it depends on how many of those data structures are being declared. thanks for any thoughts or clarification John