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

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Message-ID: <o6u6fr4znqfcznzq47jlqojdf34vdhardfypw3kl5y76pxjk6n@cxcp2mlsv62k>
Date: Tue, 17 Dec 2024 09:23:05 +0800
From: "Chia-Lin Kao (AceLan)" <acelan.kao@...onical.com>
To: Przemek Kitszel <przemyslaw.kitszel@...el.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 Mon, Dec 16, 2024 at 06:53:10AM +0100, Przemek Kitszel wrote:
> 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.
I was thinking of using -ENODEV or -ENXIO, and I forgot to generate
the patch again after I changed it to -ENXIO in the commit message.
I'll fix this in v2.
> 
> > 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.
Sure

> Please add a Fixes: tag.
I'm not sure which commit should I add Fixes to.

> Please make [PATCH iwl-net] as a subject prefix. Please CC Vitaly.
igc is an ethernet driver, should I also add iwl-net tag?

> (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.
You are right, looks like the patch fixes the issue accidentally.
Return earlier in igc_get_invariants_base() skipping the rest of the
settings. The part impacts the behavior is nvm->word_size will be 0.
And then in igc_get_hw_semaphore_i225() the timeout value will become
1. So that we won't hang for 40 seconds to wait for the timeout.

This patch is not perfect, I need to figure out another way to address
the issue better.
Please let me know if you got any ideas.
Thanks.
> 
> >   	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
>