Re: [PATCH net 3/3] igc: return early when failing to read EECD register

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Kalesh, Przemek, linux-pci]

On Tue, Jan 07, 2025 at 11:01:47AM -0800, Tony Nguyen wrote:
> From: En-Wei Wu <en-wei.wu@canonical.com>
> 
> When booting with a dock connected, the igc driver may 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.
> 
> To address this, a validation check and a corresponding return value
> catch 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 significantly improves
> boot time when using a dock with an igc NIC.
> 
> Log before the patch:
> [    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
> 
> Log after the patch:
> [    1.031000] igc 0000:70:00.0: enabling device (0000 -> 0002)
> [    1.032097] igc 0000:70:00.0: PTM enabled, 4ns granularity
> [    1.642291] igc 0000:70:00.0 (unnamed net_device) (uninitialized): PCIe link lost, device now detached
> [    5.480490] igc 0000:70:00.0: enabling device (0000 -> 0002)
> [    5.480516] igc 0000:70:00.0: PTM enabled, 4ns granularity
> 
> Fixes: ab4056126813 ("igc: Add NVM support")
> Cc: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
> Signed-off-by: En-Wei Wu <en-wei.wu@canonical.com>
> Reviewed-by: Vitaly Lifshits <vitaly.lifshits@intel.com>
> Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
> Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
> ---
>  drivers/net/ethernet/intel/igc/igc_base.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_base.c b/drivers/net/ethernet/intel/igc/igc_base.c
> index 9fae8bdec2a7..1613b562d17c 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)
>  	u32 eecd = rd32(IGC_EECD);
>  	u16 size;
>  
> +	/* failed to read reg and got all F's */
> +	if (!(~eecd))
> +		return -ENXIO;

I don't understand this.  It looks like a band-aid that makes boot
faster but doesn't solve the real problem.

In its defense, I guess that with this patch, the first igc probe
fails, and then for some reason we attempt another a few seconds
later, and the second igc probe works fine, so the NIC actually does
end up working correct, right?

I think the PCI core has some issues with configuring ASPM L1.2, and I
wonder if those are relevant here.  If somebody can repro the problem
(i.e., without this patch, which looks like it appeared in v6.13 as
bd2776e39c2a ("igc: return early when failing to read EECD
register")), I wonder if you could try booting with "pcie_port_pm=off
pcie_aspm.policy=performance" and see if that also avoids the problem?

If so, I'd like to see the dmesg log with "pci=earlydump" and the
"sudo lspci -vv" output when booted with and without "pcie_port_pm=off
pcie_aspm.policy=performance".

>  	size = FIELD_GET(IGC_EECD_SIZE_EX_MASK, eecd);
>  
>  	/* Added to a constant, "size" becomes the left-shift value
> @@ -221,6 +225,8 @@ static s32 igc_get_invariants_base(struct igc_hw *hw)
>  
>  	/* NVM initialization */
>  	ret_val = igc_init_nvm_params_base(hw);
> +	if (ret_val)
> +		goto out;
>  	switch (hw->mac.type) {
>  	case igc_i225:
>  		ret_val = igc_init_nvm_params_i225(hw);
> -- 
> 2.47.1
>