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

["Jeremy Linton" <jeremy.linton@arm.com>]

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.

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



> 
> 
> 
>> 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
>>
>>
>>
>> 
>>
>>