linux-kernel - Re: [PATCH] igc: Return early when failing to read EECD register

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Message-ID: <a1c44976-9e88-4d58-bad8-34fd397ba626@intel.com>
Date: Mon, 16 Dec 2024 06:53:10 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: "Chia-Lin Kao (AceLan)" <acelan.kao@...onical.com>
CC: Tony Nguyen <anthony.l.nguyen@...el.com>, Andrew Lunn
	<andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, <intel-wired-lan@...ts.osuosl.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Vitaly Lifshits
	<vitaly.lifshits@...el.com>
Subject: Re: [PATCH] igc: Return early when failing to read EECD register

On 12/16/24 06:14, Chia-Lin Kao (AceLan) wrote:
> When booting with a dock connected, the igc driver can get stuck for ~40
> seconds if PCIe link is lost during initialization.
> 
> This happens because the driver access device after EECD register reads
> return all F's, indicating failed reads. Consequently, hw->hw_addr is set
> to NULL, which impacts subsequent rd32() reads. This leads to the driver
> hanging in igc_get_hw_semaphore_i225(), as the invalid hw->hw_addr
> prevents retrieving the expected value.

Than you very much for the patch and the analysis!

> 
> To address this, a validation check is added for the EECD register read
> result. If all F's are returned, indicating PCIe link loss, the driver
> will return -ENXIO immediately. This avoids the 40-second hang and

It is not clear from the patch what part of the driver will return
-ENXIO, you have put -ENODEV in the patch, but it's ignored anyway.

> significantly improves boot time when using a dock with an igc NIC.
> 
> [    0.911913] igc 0000:70:00.0: enabling device (0000 -> 0002)
> [    0.912386] igc 0000:70:00.0: PTM enabled, 4ns granularity
> [    1.571098] igc 0000:70:00.0 (unnamed net_device) (uninitialized): PCIe link lost, device now detached
> [   43.449095] igc_get_hw_semaphore_i225: igc 0000:70:00.0 (unnamed net_device) (uninitialized): Driver can't access device - SMBI bit is set.
> [   43.449186] igc 0000:70:00.0: probe with driver igc failed with error -13
> [   46.345701] igc 0000:70:00.0: enabling device (0000 -> 0002)
> [   46.345777] igc 0000:70:00.0: PTM enabled, 4ns granularity
>

Would be best if you could also attach the sequence after your fix.
Please add a Fixes: tag.
Please make [PATCH iwl-net] as a subject prefix. Please CC Vitaly.
(But please also wait a day prior to sending v2 for more feedback).

> Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@...onical.com>
> ---
>   drivers/net/ethernet/intel/igc/igc_base.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_base.c b/drivers/net/ethernet/intel/igc/igc_base.c
> index 9fae8bdec2a7..54ce60280765 100644
> --- a/drivers/net/ethernet/intel/igc/igc_base.c
> +++ b/drivers/net/ethernet/intel/igc/igc_base.c
> @@ -68,6 +68,10 @@ static s32 igc_init_nvm_params_base(struct igc_hw *hw)

This function is used only in igc_get_invariants_base(), which ignores
the return value you have added. I would expect it to propagate instead.

>   	u32 eecd = rd32(IGC_EECD);
>   	u16 size;
>   
> +	/* failed to read reg and got all F's */
> +	if (!(~eecd))
> +		return -ENODEV;
> +
>   	size = FIELD_GET(IGC_EECD_SIZE_EX_MASK, eecd);
>   
>   	/* Added to a constant, "size" becomes the left-shift value