diff options
Diffstat (limited to 'drivers/net/ethernet/intel/e1000e/e1000.h')
| -rw-r--r-- | drivers/net/ethernet/intel/e1000e/e1000.h | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/drivers/net/ethernet/intel/e1000e/e1000.h b/drivers/net/ethernet/intel/e1000e/e1000.h index a187582d2299..ba9c19e6994c 100644 --- a/drivers/net/ethernet/intel/e1000e/e1000.h +++ b/drivers/net/ethernet/intel/e1000e/e1000.h @@ -360,23 +360,43 @@ s32 e1000e_get_base_timinca(struct e1000_adapter *adapter, u32 *timinca); * As a result, a shift of INCVALUE_SHIFT_n is used to fit a value of * INCVALUE_n into the TIMINCA register allowing 32+8+(24-INCVALUE_SHIFT_n) * bits to count nanoseconds leaving the rest for fractional nonseconds. + * + * Any given INCVALUE also has an associated maximum adjustment value. This + * maximum adjustment value is the largest increase (or decrease) which can be + * safely applied without overflowing the INCVALUE. Since INCVALUE has + * a maximum range of 24 bits, its largest value is 0xFFFFFF. + * + * To understand where the maximum value comes from, consider the following + * equation: + * + * new_incval = base_incval + (base_incval * adjustment) / 1billion + * + * To avoid overflow that means: + * max_incval = base_incval + (base_incval * max_adj) / billion + * + * Re-arranging: + * max_adj = floor(((max_incval - base_incval) * 1billion) / 1billion) */ #define INCVALUE_96MHZ 125 #define INCVALUE_SHIFT_96MHZ 17 #define INCPERIOD_SHIFT_96MHZ 2 #define INCPERIOD_96MHZ (12 >> INCPERIOD_SHIFT_96MHZ) +#define MAX_PPB_96MHZ 23999900 /* 23,999,900 ppb */ #define INCVALUE_25MHZ 40 #define INCVALUE_SHIFT_25MHZ 18 #define INCPERIOD_25MHZ 1 +#define MAX_PPB_25MHZ 599999900 /* 599,999,900 ppb */ #define INCVALUE_24MHZ 125 #define INCVALUE_SHIFT_24MHZ 14 #define INCPERIOD_24MHZ 3 +#define MAX_PPB_24MHZ 999999999 /* 999,999,999 ppb */ #define INCVALUE_38400KHZ 26 #define INCVALUE_SHIFT_38400KHZ 19 #define INCPERIOD_38400KHZ 1 +#define MAX_PPB_38400KHZ 230769100 /* 230,769,100 ppb */ /* Another drawback of scaling the incvalue by a large factor is the * 64-bit SYSTIM register overflows more quickly. This is dealt with |