Re: [PATCH v3 1/5] MdeModulePkg: introduce non-discoverable device protocol

["Ni, Ruiyu" <ruiyu.ni@intel.com>]

>>>>>>>> 1. Can you add "PCI" keyword into the protocol name?
>>>>>>>> e.g.: EDKII_NON_DISCOVERABLE_PCI_DEVICE_PROTOCOL_GUID
>>>>>>>>
>>>>>>>
>>>>>>> No. This protocol does not describe pci devices, and it is a peculiarity of the
>>>>>>> edk2 driver stack that some non-pci devices can only be driven by pci drivers.
>>>>>>>
>>>>>>> in other words, pci is part of the /driver/ side, and it is perfectly possible for,
>>>>>>> e.g., a non-discoverable ahci device to be driven by a different non-pci driver
>>>>>>> in the future.
>>>>>>>
>>>>>>
>>>>>> I see. So some types of devices are handled by the current
>>>>>> NonDiscoveablePciDevice driver, and some other types of devices may be
>>>>>> handled by a future NonDiscoverableXXXDevice driver.
>>>>>> Now since the AHCI type is already handled by the NonDiscoverablePciDevice
>>>>>> driver, when there is a new NonDiscoverableXXXDevice driver, how can the two
>>>>>> know whether it should manage the AHCI type device or not?
>>>>>
>>>>>Good question. But how does the UEFI driver model deal with that? What happens if i have two drivers that both support
>>>the
>>>>>Ahci Pci class codes?
>>>> PCI CFG header contains VendorID/DeviceID fields which can be used to distinguish
>>>> them.
>>>>
>>>
>>>No, that is not what I mean.
>>>
>>>Your question is how we should deal with multiple drivers that
>>>support, for instance, the AHCI non-discoverable device type. My
>>>answer is that this is not any different from a platform configuration
>>>that has more than one PCI I/O based driver that supports the AHCI PCI
>>>class codes. The UEFI driver model has priority rules and protocols to
>>>decide which driver gets precedence. I don't see how it should be any
>>>different here.
>>
>> I see they are different. Based on PciIo, the *HCI drivers can query
>> additional information from PCI CFG header, instead of just using
>> the PCI class code.
>>
>> But with the NonDiscoverableDevice protocol, there is no additional
>> information can help the *HCI drivers decide which to manage.
>>
>> I don't see any practical negative point which prevents degrading
>> NonDiscoverableDevice protocol to NonDiscoverable*Pci*Protocol.
>> After all, as I said, all *HCI drivers are based on PciIo.
>>
>
>Yes the *drivers* are based on PCI. But that does not make the
>*devices* PCI devices. That is the whole problem we are trying to deal
>with. So describing the non-PCI devices as PCI devices is incorrect
>imo. The fact that we will use PCI drivers to drive non-PCI devices is
>an implementation detail of EDK2, and is a property of the *driver*
>side not the *device* side. So using PCI class codes etc to wire up
>the correct driver should be local to the driver, and not pollute the
>description of the device.
>
>For example, if we would ever split the AHCI driver into a AHCI part
>and a PCI part (which I know is unlikely to occur), I would want the
>non-PCI AHCI driver to be used with the same protocol. Perhaps that
>means we need a protocol for each type of device rather than an enum?
>In any case, putting PCI-specific metadata into the device description
>makes the situation worse, because now both the *device* and the
>*driver* side are forced to use PCI internals to describe devices that
>have nothing to do with PCI

If I understand correctly, you want the protocol producer can simply
produce such protocol without the knowledge of PCI. I agree!
But we do need to make the protocol definition stable enough. I do not
like to see the enum type being extended in future to support more types
of devices.
1. Can you use different GUIDs for different types of devices?
2. As I replied as comment #2 to patch 3/5, do you have better way to
deal with the SDHCI Host controller driver access?


>
>Thanks,
>Ard.