6.4-stable review patch. If anyone has any objections, please let me know.
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From: Rahul Rameshbabu rrameshbabu@nvidia.com
[ Upstream commit 84a58e60038fa0366006977dba85eae16b2e3d78 ]
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 vadim.fedorenko@linux.dev 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 rrameshbabu@nvidia.com Tested-by: Vadim Fedorenko vadim.fedorenko@linux.dev Reviewed-by: Jacob Keller jacob.e.keller@intel.com Reviewed-by: Simon Horman horms@kernel.org Acked-by: Saeed Mahameed saeedm@nvidia.com Link: https://lore.kernel.org/r/20230821230554.236210-1-rrameshbabu@nvidia.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- .../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 dba4c5e2f7667..94a1635ecdd47 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/lib/clock.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/clock.c @@ -32,16 +32,13 @@
#include <linux/clocksource.h> #include <linux/highmem.h> +#include <linux/log2.h> #include <linux/ptp_clock_kernel.h> #include <rdma/mlx5-abi.h> #include "lib/eq.h" #include "en.h" #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 bool mlx5_is_mtutc_time_adj_cap(struct mlx5_core_dev *mdev, s64 delta) { s64 min = MLX5_MTUTC_OPERATION_ADJUST_TIME_MIN; @@ -910,7 +932,7 @@ 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;