Re: [edk2-devel] [PATCH 1/2] Silicon/Broadcom/BcmGenetDxe: Delay for linkup in transmit

["Ard Biesheuvel" <ardb@kernel.org>]

On Mon, 10 May 2021 at 19:26, Jeremy Linton <jeremy.linton@arm.com> wrote:
>
> Hi,
>
> On 5/10/21 11:56 AM, Ard Biesheuvel wrote:
> > On Thu, 15 Apr 2021 at 21:22, Jeremy Linton <jeremy.linton@arm.com> wrote:
> >>
> >> Under normal circumstances GenetSimpleNetworkTransmit won't be
> >> called unless the rest of the network stack detects the link is
> >> up. So, during normal operation when the adapter is initialized
> >> the link naturally transitions to link up, and then is ready for
> >> activity later in the boot sequence. If that hasn't happened by
> >> the time PXE runs then it will itself wait for the link.
> >>
> >> OTOH, the normal distro PXE sequence involves PXE loading shim
> >> which in turn loads grub, which tries to read machine specific
> >> configs, modules, and grub.cfg in order to prepare the boot menu.
> >> Then, once a grub selection is picked, it might try to load the
> >> kernel+initrd.
> >>
> >> In this sequence the network stack is shutdown and restarted
> >> multiple times. Grub though, starts up, notices its been network
> >> booted, reads saved network parameters and immediately tries to
> >> transmit data assuming the link is still up.
> >>
> >> When that happens grub will print "couldn't send network packet"
> >> and if that lasts long enough it fails to load grub.cfg and the
> >> user gets dropped to the grub prompt because no one in the path
> >> bothers to assure the link state has transitioned back up.
> >>
> >
> > This is an excellent problem description. Could we dedicate a couple
> > of paragraphs to the solution as well? Especially given that 'wait for
> > random # of seconds' seems to be the taken approach here, which seems
> > a bit sloppy to me, given that we should be able to detect whether the
> > link is up, no?
>
> Isn't that what GenericPhyUpdateConfig is doing? Checking for linkup,
> and updating the phy state? So once the link goes up, it return
> EFI_SUCCESS and the loop terminates.
>

OK. Could you dedicate some prose to this logic in the commit log please?

> I was actually a bit concerned that the 10s wasn't enough since AFAIK a
> large part of the delay is the remote side.
>

The remote side of what? The Ethernet cable?

>
>
> >
> >
> >
> >> For reference: https://github.com/pftf/RPi4/issues/113
> >>
> >> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> >> ---
> >>   .../Drivers/Net/BcmGenetDxe/SimpleNetwork.c        | 24 ++++++++++++++++++++--
> >>   1 file changed, 22 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/SimpleNetwork.c b/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/SimpleNetwork.c
> >> index 1bda18f157..29c76d8495 100644
> >> --- a/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/SimpleNetwork.c
> >> +++ b/Silicon/Broadcom/Drivers/Net/BcmGenetDxe/SimpleNetwork.c
> >> @@ -13,6 +13,7 @@
> >>   #include <Library/DebugLib.h>
> >>   #include <Library/DmaLib.h>
> >>   #include <Library/NetLib.h>
> >> +#include <Library/UefiBootServicesTableLib.h>
> >>   #include <Protocol/SimpleNetwork.h>
> >>
> >>   #include "BcmGenetDxe.h"
> >> @@ -590,9 +591,28 @@ GenetSimpleNetworkTransmit (
> >>
> >>     if (!Genet->SnpMode.MediaPresent) {
> >>       //
> >> -    // Don't bother transmitting if there's no link.
> >> +    // We should only really get here if the link was up
> >> +    // and is now down due to a stop/shutdown sequence, and
> >> +    // the app (grub) doesn't bother to check link state
> >> +    // because it was up a moment before.
> >> +    // Lets wait a bit for the link to resume, rather than
> >> +    // failing to send. In the case of grub it works either way
> >> +    // but we can't be sure that is universally true, and
> >> +    // hanging for a couple seconds is nicer than a screen of
> >> +    // grub send failure messages.
> >>       //
> >> -    return EFI_NOT_READY;
> >> +    int retries = 1000;
> >> +    DEBUG ((DEBUG_INFO, "%a: Waiting 10s for link\n", __FUNCTION__));
> >> +    do {
> >> +      gBS->Stall (10000);
> >> +      Status = GenericPhyUpdateConfig (&Genet->Phy);
> >> +    } while (EFI_ERROR (Status) && retries--);
> >> +    if (EFI_ERROR (Status)) {
> >> +      DEBUG ((DEBUG_ERROR, "%a: no link\n", __FUNCTION__));
> >> +      return EFI_NOT_READY;
> >> +    } else {
> >> +      Genet->SnpMode.MediaPresent = TRUE;
> >> +    }
> >>     }
> >>
> >>     if (HeaderSize != 0) {
> >> --
> >> 2.13.7
> >>
> >>
> >>
> >> 
> >>
> >>
>