Re: SNP_INIT while in TPL_NOTIFY

["Tomas Pilar (tpilar)" <tpilar@solarflare.com>]

Thanks Laszlo,

I am glad I wasn't going insane there. I'll turn it into a simple busy poll.

Cheers,
Tom


On 27/01/17 18:12, Laszlo Ersek wrote:
> On 01/27/17 17:51, Tomas Pilar (tpilar) wrote:
>> Hi,
>>
>> I am currently maintaining our network driver written using the EDKII
>> framework. Our network device implements a MCDI (mc-driver interface)
>> which is (in theory) asynchronous (DMA doorbell-messagebox
>> communication), although the majority of the calls take less than a
>> jiffy. So for example, the setting up of TX and RX queues on the NIC
>> requires some MCDI calls which the driver then has to wait for. I've
>> implemented this using the gSB->SetTimer event system.
>>
>> My problem is that the SimpleNetworkInitialize() method is called by the
>> UEFI platform network core (network core finds a new NIC with SNP ->
>> tries to open -> not initialised, so it tries to INIT) using a
>> TPL_NOTIFY context,
> This looks like a bug, in the code that calls SimpleNetworkInitialize().
> According to "Table 24. TPL Restrictions", for Simple Network Protocol
> methods, the TPL must be <= TPL_CALLBACK. Meaning, an SNP implementation
> mustn't raise the TPL above TPL_CALLBACK, but also that any client can't
> call SNP methods while executing on a TPL > TPL_CALLBACK.
>
> Worse, even staying at TPL_CALLBACK wouldn't be good enough for calling
> gBS->SetTimer(). SetTimer is < TPL_HIGH_LEVEL, so that'd be fine, but
> gBS->WaitForEvent() is strictly = TPL_APPLICATION. So WaitForEvent()
> can't be called when running on TPL_CALLBACK level.
>
>> where the code is not allowed to sleep (I assume
>> that this is the MNP generic one second network poll timer). I could in
>> theory initialise the NIC earlier, during probe, but the SNP allows for
>> specification of extra buffer space for TX and RX during init. The
>> network core might conceivable use that. Or the MNP might want to change
>> station address using SNP or call for a reset which again requires
>> asynchronous NIC operation.
>>
>> Has anyone encountered something similar? Is there a canonical solution
>> to this issue?
> I think you can poll the NIC in a busy loop, or if that's excessive, use
> gBS->Stall() between polls. Stall() is <= TPL_HIGH_LEVEL, so it should
> be safe. OTOH, "Execution of the processor is not yielded for the
> duration of the stall".
>
> Thanks
> Laszlo
>
>> Cheers,
>> Tomas Pilar
>>
>>
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