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Commit 830e0dd9 authored by Jacob Keller's avatar Jacob Keller Committed by Jeff Kirsher
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i40e: avoid overflow in i40e_ptp_adjfreq() 



When operating at 1GbE, the base incval for the PTP clock is so large
that multiplying it by numbers close to the max_adj can overflow the
u64.

Rather than attempting to limit the max_adj to a value small enough to
avoid overflow, instead calculate the incvalue adjustment based on the
40GbE incvalue, and then multiply that by the scaling factor for the
link speed.

This sacrifices a small amount of precision in the adjustment but we
avoid erratic behavior of the clock due to the overflow caused if ppb is
very near the maximum adjustment.

Signed-off-by: default avatarJacob Keller <jacob.e.keller@intel.com>
Tested-by: default avatarAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: default avatarJeff Kirsher <jeffrey.t.kirsher@intel.com>
parent 5305d0fe

drivers/net/ethernet/intel/i40e/i40e.h

+1 −1
Original line number Diff line number Diff line
@@ -586,7 +586,7 @@ struct i40e_pf { 
	unsigned long ptp_tx_start;

	struct hwtstamp_config tstamp_config;

	struct mutex tmreg_lock; /* Used to protect the SYSTIME registers. */

	u64 ptp_base_adj;

	u32 ptp_adj_mult;

	u32 tx_hwtstamp_timeouts;

	u32 tx_hwtstamp_skipped;

	u32 rx_hwtstamp_cleared;

drivers/net/ethernet/intel/i40e/i40e_ptp.c

+27 −14
Original line number Diff line number Diff line
@@ -17,8 +17,8 @@ 
 * 1588 functionality is not supported at 100Mbps.

 */

#define I40E_PTP_40GB_INCVAL		0x0199999999ULL

#define I40E_PTP_10GB_INCVAL 0x0333333333ULL

#define I40E_PTP_1GB_INCVAL  0x2000000000ULL

#define I40E_PTP_10GB_INCVAL_MULT	2

#define I40E_PTP_1GB_INCVAL_MULT	20



#define I40E_PRTTSYN_CTL1_TSYNTYPE_V1  BIT(I40E_PRTTSYN_CTL1_TSYNTYPE_SHIFT)

#define I40E_PRTTSYN_CTL1_TSYNTYPE_V2  (2 << \
@@ -106,17 +106,24 @@ static int i40e_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb) 
		ppb = -ppb;

	}



	smp_mb(); /* Force any pending update before accessing. */

	adj = READ_ONCE(pf->ptp_base_adj);



	freq = adj;

	freq = I40E_PTP_40GB_INCVAL;

	freq *= ppb;

	diff = div_u64(freq, 1000000000ULL);



	if (neg_adj)

		adj -= diff;

		adj = I40E_PTP_40GB_INCVAL - diff;

	else

		adj += diff;

		adj = I40E_PTP_40GB_INCVAL + diff;



	/* At some link speeds, the base incval is so large that directly

	 * multiplying by ppb would result in arithmetic overflow even when

	 * using a u64. Avoid this by instead calculating the new incval

	 * always in terms of the 40GbE clock rate and then multiplying by the

	 * link speed factor afterwards. This does result in slightly lower

	 * precision at lower link speeds, but it is fairly minor.

	 */

	smp_mb(); /* Force any pending update before accessing. */

	adj *= READ_ONCE(pf->ptp_adj_mult);



	wr32(hw, I40E_PRTTSYN_INC_L, adj & 0xFFFFFFFF);

	wr32(hw, I40E_PRTTSYN_INC_H, adj >> 32);
@@ -438,6 +445,7 @@ void i40e_ptp_set_increment(struct i40e_pf *pf) 
	struct i40e_link_status *hw_link_info;

	struct i40e_hw *hw = &pf->hw;

	u64 incval;

	u32 mult;



	hw_link_info = &hw->phy.link_info;
@@ -445,10 +453,10 @@ void i40e_ptp_set_increment(struct i40e_pf *pf) 


	switch (hw_link_info->link_speed) {

	case I40E_LINK_SPEED_10GB:

		incval = I40E_PTP_10GB_INCVAL;

		mult = I40E_PTP_10GB_INCVAL_MULT;

		break;

	case I40E_LINK_SPEED_1GB:

		incval = I40E_PTP_1GB_INCVAL;

		mult = I40E_PTP_1GB_INCVAL_MULT;

		break;

	case I40E_LINK_SPEED_100MB:

	{
@@ -459,15 +467,20 @@ void i40e_ptp_set_increment(struct i40e_pf *pf) 
				 "1588 functionality is not supported at 100 Mbps. Stopping the PHC.\n");

			warn_once++;

		}

		incval = 0;

		mult = 0;

		break;

	}

	case I40E_LINK_SPEED_40GB:

	default:

		incval = I40E_PTP_40GB_INCVAL;

		mult = 1;

		break;

	}



	/* The increment value is calculated by taking the base 40GbE incvalue

	 * and multiplying it by a factor based on the link speed.

	 */

	incval = I40E_PTP_40GB_INCVAL * mult;



	/* Write the new increment value into the increment register. The

	 * hardware will not update the clock until both registers have been

	 * written.
@@ -476,7 +489,7 @@ void i40e_ptp_set_increment(struct i40e_pf *pf) 
	wr32(hw, I40E_PRTTSYN_INC_H, incval >> 32);



	/* Update the base adjustement value. */

	WRITE_ONCE(pf->ptp_base_adj, incval);

	WRITE_ONCE(pf->ptp_adj_mult, mult);

	smp_mb(); /* Force the above update. */

}