From 84a58e60038fa0366006977dba85eae16b2e3d78 Mon Sep 17 00:00:00 2001 From: Rahul Rameshbabu Date: Mon, 21 Aug 2023 16:05:54 -0700 Subject: [PATCH] net/mlx5: Dynamic cyclecounter shift calculation for PTP free running clock Use a dynamic calculation to determine the shift value for the internal timer cyclecounter that will lead to the highest precision frequency adjustments. Previously used a constant for the shift value assuming all devices supported by the driver had a nominal frequency of 1GHz. However, there are devices that operate at different frequencies. The previous shift value constant would break the PHC functionality for those devices. Reported-by: Vadim Fedorenko Closes: https://lore.kernel.org/netdev/20230815151507.3028503-1-vadfed@meta.com/ Fixes: 6a4010927562 ("net/mlx5: Update cyclecounter shift value to improve ptp free running mode precision") Signed-off-by: Rahul Rameshbabu Tested-by: Vadim Fedorenko Reviewed-by: Jacob Keller Reviewed-by: Simon Horman Acked-by: Saeed Mahameed Link: https://lore.kernel.org/r/20230821230554.236210-1-rrameshbabu@nvidia.com Signed-off-by: Jakub Kicinski --- .../net/ethernet/mellanox/mlx5/core/lib/clock.c | 32 ++++++++++++++++++---- 1 file changed, 27 insertions(+), 5 deletions(-) diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/clock.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/clock.c index 377372f..aa29f09 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/lib/clock.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/clock.c @@ -32,6 +32,7 @@ #include #include +#include #include #include #include "lib/eq.h" @@ -39,10 +40,6 @@ #include "clock.h" enum { - MLX5_CYCLES_SHIFT = 31 -}; - -enum { MLX5_PIN_MODE_IN = 0x0, MLX5_PIN_MODE_OUT = 0x1, }; @@ -93,6 +90,31 @@ static bool mlx5_modify_mtutc_allowed(struct mlx5_core_dev *mdev) return MLX5_CAP_MCAM_FEATURE(mdev, ptpcyc2realtime_modify); } +static u32 mlx5_ptp_shift_constant(u32 dev_freq_khz) +{ + /* Optimal shift constant leads to corrections above just 1 scaled ppm. + * + * Two sets of equations are needed to derive the optimal shift + * constant for the cyclecounter. + * + * dev_freq_khz * 1000 / 2^shift_constant = 1 scaled_ppm + * ppb = scaled_ppm * 1000 / 2^16 + * + * Using the two equations together + * + * dev_freq_khz * 1000 / 1 scaled_ppm = 2^shift_constant + * dev_freq_khz * 2^16 / 1 ppb = 2^shift_constant + * dev_freq_khz = 2^(shift_constant - 16) + * + * then yields + * + * shift_constant = ilog2(dev_freq_khz) + 16 + */ + + return min(ilog2(dev_freq_khz) + 16, + ilog2((U32_MAX / NSEC_PER_MSEC) * dev_freq_khz)); +} + static s32 mlx5_ptp_getmaxphase(struct ptp_clock_info *ptp) { struct mlx5_clock *clock = container_of(ptp, struct mlx5_clock, ptp_info); @@ -909,7 +931,7 @@ static void mlx5_timecounter_init(struct mlx5_core_dev *mdev) dev_freq = MLX5_CAP_GEN(mdev, device_frequency_khz); timer->cycles.read = read_internal_timer; - timer->cycles.shift = MLX5_CYCLES_SHIFT; + timer->cycles.shift = mlx5_ptp_shift_constant(dev_freq); timer->cycles.mult = clocksource_khz2mult(dev_freq, timer->cycles.shift); timer->nominal_c_mult = timer->cycles.mult; -- 2.7.4