Re: [Intel-wired-lan] [PATCH 1/2] igc: Wait for MAC passthrough after reset

["Chia-Lin Kao \(AceLan\) via Intel-wired-lan" <intel-wired-lan@osuosl.org>]

On Mon, Jun 29, 2026 at 07:42:43PM +0300, Ruinskiy, Dima wrote:
> Hi AceLan,
>
> Some more comments below.
>
> On 22/06/2026 4:57, Chia-Lin Kao (AceLan) wrote:
>
> > >
> > > Because 100 iterations of 100msec each - this translates to up-to 10
> > > seconds, no?
> > Yes, just in case it takes longer.
> > I think 5 seconds should be enough if you feel this is feasible.
> 5 seconds also sounds excessive, assuming the majority of the systems do not
> support / enable MAC passthrough via the FW feature (and I have a hunch it
> is the case). 2 seconds... maybe, but then you say that in some rare cases
> it exceeds 2 seconds as well. What if in some even rare cases it exceeds
> 5/10 seconds? Perhaps because of some glitch it will not come up at all on
> this cycle. Should the driver always wait?
>
> > I wish we can detect if the MAC passthrough is enabled, so that we
> > know if we need to poll for the MAC address.
> Unfortunately, like you I am not aware of any way for the driver to know
> whether MAC passthrough via FW is enabled. Because of this we have been
> exploring a simpler way to support this feature via ACPI objects (which are
> set by the BIOS when MAC passthrough is enabled and are easy for the driver
> to query). I know some vendors have already implemented it, and I am
> currently drafting a patch to send.
Any good news about this patch?

>
> > For the FW interrupt mechanism also needs BIOS support, and we don't
> > have the power to push this.
> The mechanism I have in mind does not require BIOS support - the I225/I226
> FW already supports the required interrupt, AFAIK - it merely needs to be
> enabled in the igc driver. With that said, there still remains the question
> of how to notify the network stack above us that the MAC address has changed
> post-probe - and whether it is even supported.
>
> --Dima
>
> >
> > >
> > > Thanks,
> > > Dima.
> > >
> > > >
> > > > > Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
> > > > > ---
> > > > >    drivers/net/ethernet/intel/igc/igc_main.c | 48
> > > > > +++++++++++++++++++++++
> > > > >    1 file changed, 48 insertions(+)
> > > > >
> > > > > diff --git a/drivers/net/ethernet/intel/igc/igc_main.c
> > > > > b/drivers/net/ethernet/intel/igc/igc_main.c
> > > > > index 2c9e2dfd8499..fa9752ed8bc5 100644
> > > > > --- a/drivers/net/ethernet/intel/igc/igc_main.c
> > > > > +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> > > > > @@ -11,6 +11,7 @@
> > > > >    #include <net/pkt_sched.h>
> > > > >    #include <linux/bpf_trace.h>
> > > > >    #include <net/xdp_sock_drv.h>
> > > > > +#include <linux/etherdevice.h>
> > > > >    #include <linux/pci.h>
> > > > >    #include <linux/mdio.h>
> > > > >
> > > > > @@ -69,6 +70,52 @@ static const struct pci_device_id igc_pci_tbl[] = {
> > > > >
> > > > >    MODULE_DEVICE_TABLE(pci, igc_pci_tbl);
> > > > >
> > > > > +static void igc_read_rar0(struct igc_hw *hw, u8 *addr, u32 *ral, u32
> > > > > +*rah) {
> > > > > +	*ral = rd32(IGC_RAL(0));
> > > > > +	*rah = rd32(IGC_RAH(0));
> > > > > +
> > > > > +	addr[0] = *ral & 0xff;
> > > > > +	addr[1] = (*ral >> 8) & 0xff;
> > > > > +	addr[2] = (*ral >> 16) & 0xff;
> > > > > +	addr[3] = (*ral >> 24) & 0xff;
> > > > > +	addr[4] = *rah & 0xff;
> > > > > +	addr[5] = (*rah >> 8) & 0xff;
> > > > > +}
> > > > > +
> > > > > +static bool igc_is_lmvp_device(struct pci_dev *pdev) {
> > > > > +	switch (pdev->device) {
> > > > > +	case IGC_DEV_ID_I225_LMVP:
> > > > > +	case IGC_DEV_ID_I226_LMVP:
> > > > > +		return true;
> > > > > +	default:
> > > > > +		return false;
> > > > > +	}
> > > > > +}
> > > > > +
> > > > > +static void igc_wait_for_lmvp_mac_passthrough(struct pci_dev *pdev,
> > > > > +					      struct igc_hw *hw)
> > > > > +{
> > > > > +	u8 addr[ETH_ALEN] __aligned(2);
> > > > > +	u32 orig_ral, orig_rah;
> > > > > +	u32 ral, rah;
> > > > > +	int i;
> > > > > +
> > > > > +	if (!igc_is_lmvp_device(pdev))
> > > > > +		return;
> > > > > +
> > > > > +	igc_read_rar0(hw, addr, &orig_ral, &orig_rah);
> > > > > +
> > > > > +	for (i = 0; i < 100; i++) {
> > > > > +		msleep(100);
> > > > > +		igc_read_rar0(hw, addr, &ral, &rah);
> > > > > +		if ((ral != orig_ral || rah != orig_rah) &&
> > > > > +		    is_valid_ether_addr(addr))
> > > > > +			return;
> > > > > +	}
> > > > > +}
> > > > > +
> > > > >    enum latency_range {
> > > > >    	lowest_latency = 0,
> > > > >    	low_latency = 1,
> > > > > @@ -7259,6 +7306,7 @@ static int igc_probe(struct pci_dev *pdev,
> > > > >    	 * known good starting state
> > > > >    	 */
> > > > >    	hw->mac.ops.reset_hw(hw);
> > > > > +	igc_wait_for_lmvp_mac_passthrough(pdev, hw);
> > > > >
> > > > >    	if (igc_get_flash_presence_i225(hw)) {
> > > > >    		if (hw->nvm.ops.validate(hw) < 0) {
> > > > > --
> > > > > 2.53.0
> > > >
> > >
>