netdev - RE: [net-next 4/4] i40e: Add a check to see if MFS is set

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Date:   Tue, 21 Apr 2020 19:44:56 +0000
From:   "Fujinaka, Todd" <todd.fujinaka@...el.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "sassmann@...hat.com" <sassmann@...hat.com>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Bowers, AndrewX" <andrewx.bowers@...el.com>
Subject: RE: [net-next 4/4] i40e: Add a check to see if MFS is set

Sorry for the top-posting. Outlook. I can't seem to find this email on my non-Windows machine.

I don't know why we don't reset the NIC, but I was told there is a reason. And the reason there's an index is because
the datasheet shows four registers. Somehow while I was formatting that long line I lost the math bits that read four
different registers. Let me see if I can fix this patch.

Todd Fujinaka
Software Application Engineer
Data Center Group
Intel Corporation
todd.fujinaka@...el.com

-----Original Message-----
From: Jakub Kicinski <kuba@...nel.org> 
Sent: Tuesday, April 21, 2020 11:00 AM
To: Kirsher, Jeffrey T <jeffrey.t.kirsher@...el.com>
Cc: davem@...emloft.net; Fujinaka, Todd <todd.fujinaka@...el.com>; netdev@...r.kernel.org; nhorman@...hat.com; sassmann@...hat.com; Brandeburg, Jesse <jesse.brandeburg@...el.com>; Bowers, AndrewX <andrewx.bowers@...el.com>
Subject: Re: [net-next 4/4] i40e: Add a check to see if MFS is set

On Mon, 20 Apr 2020 18:49:32 -0700 Jeff Kirsher wrote:
> From: Todd Fujinaka <todd.fujinaka@...el.com>
> 
> A customer was chain-booting to provision his systems and one of the 
> steps was setting MFS. MFS isn't cleared by normal warm reboots 
> (clearing requires a GLOBR) and there was no indication of why Jumbo 
> Frame receives were failing.
> 
> Add a warning if MFS is set to anything lower than the default.
> 
> Signed-off-by: Todd Fujinaka <todd.fujinaka@...el.com>
> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
> Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c 
> b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index 4c414208a22a..3fdbfede0b87 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -15347,6 +15347,15 @@ static int i40e_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  			i40e_stat_str(&pf->hw, err),
>  			i40e_aq_str(&pf->hw, pf->hw.aq.asq_last_status));
>  
> +	/* make sure the MFS hasn't been set lower than the default */ 
> +#define MAX_FRAME_SIZE_DEFAULT 0x2600
> +	for (i = 0; i < 4; i++) {

Why is this a loop? AFAICS @i is only used in the warning message

> +		val = ((rd32(&pf->hw, I40E_PRTGL_SAH) & I40E_PRTGL_SAH_MFS_MASK)
> +			>> I40E_PRTGL_SAH_MFS_SHIFT);

outer parens unnecessary

> +		if (val < MAX_FRAME_SIZE_DEFAULT)
> +			dev_warn(&pdev->dev, "MFS for port %x has been set below the 
> +default: %x\n", i, val);

Shouldn't you just reset it to default at this point? If the value is not reset on warm boot this is not really a surprise.

> +	}
> +
>  	/* Add a filter to drop all Flow control frames from any VSI from being
>  	 * transmitted. By doing so we stop a malicious VF from sending out
>  	 * PAUSE or PFC frames and potentially controlling traffic for other