From: Andrew Fish <afish@apple.com>
To: Laszlo Ersek <lersek@redhat.com>
Cc: "Tomas Pilar (tpilar)" <tpilar@solarflare.com>,
"edk2-devel@lists.01.org" <edk2-devel@ml01.01.org>
Subject: Re: SNP_INIT while in TPL_NOTIFY
Date: Mon, 30 Jan 2017 09:51:16 -0800 [thread overview]
Message-ID: <4635C152-5C77-4A3D-ADE3-B322F7EB87C0@apple.com> (raw)
In-Reply-To: <cf34540c-4585-bf35-fea4-0cf1b5d89781@redhat.com>
> On Jan 27, 2017, at 10:12 AM, Laszlo Ersek <lersek@redhat.com> 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".
>
Laszlo,
You are correct Stall() does not yield. The only way to yield from an event is to return from the event function.
When your are writing threaded code you think of stall as a way to yield, so you encoded the logic of the program as a loop that yields to the thread. In the event model, since you have to return, the idiom is not a loop but a state machine. Thus your event will yield by returning so you would want to perhaps take a different action the next time you enter the event based on previous state. So if you had to deal with a long stall you might want to program a timer event that periodically checks for the event and it will always return quickly regardless of the state of the check. So you can break stuff up into smaller events or have a single event that remembers state, but both of these are a lot like solving the problem with a state machine vs. a code loop.
Thanks,
Andrew Fish
> Thanks
> Laszlo
>
>>
>> Cheers,
>> Tomas Pilar
>>
>>
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next prev parent reply other threads:[~2017-01-30 17:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-27 16:51 SNP_INIT while in TPL_NOTIFY Tomas Pilar (tpilar)
2017-01-27 18:12 ` Laszlo Ersek
2017-01-30 10:51 ` Tomas Pilar (tpilar)
2017-01-30 17:51 ` Andrew Fish [this message]
2017-02-06 6:10 ` Ye, Ting
2017-02-06 14:58 ` Tomas Pilar (tpilar)
2017-02-07 3:31 ` Ye, Ting
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