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

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

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?



> 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
>
>
>
> 
>
>