Re: SNP_INIT while in TPL_NOTIFY

["Ye, Ting" <ting.ye@intel.com>]

Hi Tom,

Thanks for the clarification. I just want to confirm that it is not a bug in the common SNP driver. 

Best Regards,
Ye Ting

-----Original Message-----
From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Tomas Pilar (tpilar)
Sent: Monday, February 06, 2017 10:59 PM
To: Ye, Ting <ting.ye@intel.com>; Laszlo Ersek <lersek@redhat.com>; edk2-devel@lists.01.org <edk2-devel@ml01.01.org>
Subject: Re: [edk2] SNP_INIT while in TPL_NOTIFY

This is the specific implementation of SNP for our driver. We expose this implementation which is then consumed by MNP so that our NIC can be used as a NIC. The specific problem is that some functionality that SNP needs to implement (initializing queues, changing MAC, resetting) are asynchronous, but MNP can call our SNP implementation in raised TPL where one is not allowed to wait.

So the only solution seems to be to use a busy poll and actually hang the execution until the asynchronous call to the MC on the NIC is completed, even though we've been called in TPL_CALLBACK or TPL_NOTIFY.

Cheers,
Tom

On 06/02/17 06:10, Ye, Ting wrote:
> May I ask which SNP module are we discussing here?  Is it the common SnpDxe driver under MdeModulePkg/Universal/Network, or a specific driver implemented for your network device?
>
> Best Regards,
> Ye Ting
>
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of 
> Laszlo Ersek
> Sent: Saturday, January 28, 2017 2:12 AM
> To: Tomas Pilar (tpilar) <tpilar@solarflare.com>; 
> edk2-devel@lists.01.org <edk2-devel@ml01.01.org>
> Subject: Re: [edk2] SNP_INIT while in TPL_NOTIFY
>
> 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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