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

Samer El-Haj-Mahmoud

+Ard's new e-mail address

-----Original Message-----
From: Jeremy Linton <>
Sent: Thursday, April 15, 2021 3:22 PM
Cc: Ard Biesheuvel <>;;; Samer El-Haj-Mahmoud <Samer.El-Haj->; Andrei Warkentin (
<>; Jeremy Linton <>
Subject: [PATCH 1/2] Silicon/Broadcom/BcmGenetDxe: Delay for linkup in

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

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.

For reference:

Signed-off-by: Jeremy Linton <>
.../Drivers/Net/BcmGenetDxe/SimpleNetwork.c | 24
1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/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) {
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