netdev - Re: [Intel-wired-lan] [PATCH] e1000e: fix timing for 82579 Gigabit Ethernet controller

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Message-ID: <923e61cf-5f95-1662-2f4c-fc146359ab48@intel.com>
Date:   Sun, 19 Feb 2017 14:55:06 +0200
From:   "Neftin, Sasha" <sasha.neftin@...el.com>
To:     Bernd Faust <berndfaust@...il.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Yanir Lubetkin <yanirx.lubetkin@...el.com>,
        intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH] e1000e: fix timing for 82579 Gigabit
 Ethernet controller

On 2/16/2017 20:42, Bernd Faust wrote:
> After an upgrade to Linux kernel v4.x the hardware timestamps of the
> 82579 Gigabit Ethernet Controller are different than expected.
> The values that are being read are almost four times as big as before
> the kernel upgrade.
>
> The difference is that after the upgrade the driver sets the clock
> frequency to 25MHz, where before the upgrade it was set to 96MHz. Intel
> confirmed that the correct frequency for this network adapter is 96MHz.
>
> Signed-off-by: Bernd Faust <berndfaust@...il.com>
> ---
>   drivers/net/ethernet/intel/e1000e/netdev.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
> index 7017281..8b7113d 100644
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> @@ -3511,6 +3511,12 @@ s32 e1000e_get_base_timinca(struct e1000_adapter *adapter, u32 *timinca)
>
>   	switch (hw->mac.type) {
>   	case e1000_pch2lan:
> +		/* Stable 96MHz frequency */
> +		incperiod = INCPERIOD_96MHz;
> +		incvalue = INCVALUE_96MHz;
> +		shift = INCVALUE_SHIFT_96MHz;
> +		adapter->cc.shift = shift + INCPERIOD_SHIFT_96MHz;
> +		break;
>   	case e1000_pch_lpt:
>   		if (er32(TSYNCRXCTL) & E1000_TSYNCRXCTL_SYSCFI) {
>   			/* Stable 96MHz frequency */
> --
> 2.7.4
> _______________________________________________
> Intel-wired-lan mailing list
> Intel-wired-lan@...ts.osuosl.org
> http://lists.osuosl.org/mailman/listinfo/intel-wired-lan

Hello,

e1000_pch2lan mac type corresponds to 82579LM and 82579V network 
adapters. System clock frequency indication (SYSCFI) for these devices 
supports both 25MHz and 96MHz frequency. By default TSYNCRXCTL.SYSCFI is 
set to 1 and that means 96MHz frequency is picked.

It is better to keep the current implementation as it covers all options.

Thanks,

Sasha

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