Re: UEFI_DRIVER dependencies

[Andrew Fish <afish@apple.com>]

> On May 17, 2017, at 10:42 PM, Michael Zimmermann <sigmaepsilon92@gmail.com> wrote:
> 
> Michael, that's a good point but it only works for drivers which bind
> to a device. If you're just installing a protocol e.g. for virtual
> devices or special services which you don't want to turn into
> libraries then this doesn't work.
> 
> Haojian, that's what I was thinking, I just wasn't sure if the order
> is reliable.
> 

Micheal,

>From a PI/UEFI architectural perspective the contract is the depex are honored. If multiple drivers are TRUE at the same time the order they execute is not defined. Basically it is implementation choice and you should not write code that depends on this. This is why the A priori file exists, it is the only architectural way to force order of dispatch. Well DXE has BEFORE and AFTER. 

When I wrote the original dispatcher I ended up adding new drivers to the tail of the list vs. the head. Both would have been legal from a spec point of view. So by observing the current behavior you are conflating my implementation choice with the contract provided by specification. 


> Andrew, your description sounds like its about DXE_DRIVERs and their
> Depex sections, does this apply to UEFI_DRIVERs too when they're
> auto-loaded from the fdf(since they don't support the Depex section)?
> 

No Depex section for UEFI_DRIVERS implies this Depex:

[Depex]
  gEfiSecurityArchProtocolGuid          AND 
  gEfiCpuArchProtocolGuid               AND 
  gEfiMetronomeArchProtocolGuid         AND 
  gEfiTimerArchProtocolGuid             AND 
  gEfiBdsArchProtocolGuid               AND 
  gEfiWatchdogTimerArchProtocolGuid     AND 
  gEfiRuntimeArchProtocolGuid           AND 
  gEfiVariableArchProtocolGuid          AND 
  gEfiVariableWriteArchProtocolGuid     AND 
  gEfiCapsuleArchProtocolGuid           AND 
  gEfiMonotonicCounterArchProtocolGuid  AND 
  gEfiResetArchProtocolGuid             AND 
  gEfiRealTimeClockArchProtocolGuid   

This is how we glued PI (DXE_DRIVERS) and UEFI (UEFI_DRIVER) together. EFI predates the concept of DXE in PI. 

The primary job of DXE_DRIVERS is to configure all the hardware required to provide all the EFI Boot and Runtime Services. The above protocols are what the DXE Core requires to produce all the EFI Boot and Runtime services. 

Thanks,

Andrew Fish

> Thanks for all your answers,
> Michael
> 
> On Thu, May 18, 2017 at 7:21 AM, Andrew Fish <afish@apple.com> wrote:
>> 
>>> On May 17, 2017, at 10:00 PM, Kinney, Michael D <michael.d.kinney@intel.com> wrote:
>>> 
>>> Michael,
>>> 
>>> The UEFI Driver Model and the Driver Binding Protocol
>>> provide support for this case.  The idea is that a driver
>>> is loaded and started, but when a UEFI Driver is started,
>>> it only registers a Driver Binding Protocol.  Then in the
>>> BDS phase, the devices required to boot are started using
>>> the UEFI Boot Service ConnectController() and
>>> ConnectController() calls the Driver Binding Protocol(s).
>>> 
>>> The dependencies between UEFI Drivers are in their Driver
>>> Binding Protocols which are not used until after all of
>>> the UEFI Drivers are loaded and started.
>>> 
>> 
>> Micheal,
>> 
>> 1st off no dependency is really a dependency on all the architecture protocols, which is a fancy way of saying all the EFI Boot and Runtime Services are available.
>> 
>> Lets say you have a driver that depends on DiskIo. The DiskIo driver depends on BlockIo. Now what happens when a disk driver is connected and produces a BlockIO is the DiskIo driver can know get connected. The DXE Core knows a protocol was added to the handle so it will keep trying to connect drivers to that handle as long as new protocols get added. So this is how the DriverBinding Support() is used to resolve the sequence issues.
>> 
>> Thanks,
>> 
>> Andrew Fish
>> 
>>> Mike
>>> 
>>>> -----Original Message-----
>>>> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Michael
>>>> Zimmermann
>>>> Sent: Wednesday, May 17, 2017 9:43 PM
>>>> To: edk2-devel-01 <edk2-devel@lists.01.org>; Zeng, Star <star.zeng@intel.com>; Dong,
>>>> Eric <eric.dong@intel.com>
>>>> Subject: [edk2] UEFI_DRIVER dependencies
>>>> 
>>>> I know that UEFI_DRIVERs don't need or support Depex sections, but
>>>> what if an UEFI_DRIVER depends on a protocol provided by another
>>>> UEFI_DRIVER?
>>>> Since they get loaded automatically because I put them in my
>>>> platform's fdf, it raises the question of the loading order.
>>>> 
>>>> Will they get loaded in the order they're defined? How often will the
>>>> core retry if one of the drivers returns EFI_NOT_READY?
>>>> 
>>>> Thanks,
>>>> Michael
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