Re: [RFC] ACPI table HID/CID allocation

[Daniel Thompson <daniel.thompson@linaro.org>]

On 21/11/17 18:10, Udit Kumar wrote:
> Thanks Ard,
> For internal SOC devices, this is perfectly ok to drop PRP0001 from CID.
> 
>> This could be a valid reason to use PRP0001 + compatible, for things like I2C
>> slaves that are external to the SoC
> 
> For external devices (for which HID is not available), you suggest to go
> with PRP0001 + compatible or that device driver needs add ACPI HID support.

I don't think internal or external to the SoC would be any kind of 
deciding factor in how to best to bind, simply because I don't 
understand why there is no HID available.

Large OEMs and board manufacturers usually have their own vendor IDs and 
sometimes have to use these to describe hardware (IIRC the SMC LAN9xxx 
on the ARM Juno uses an ARM HID).

Admittedly the part you are describing follows a JEDEC standard so it 
would be nice to have more widely agreed bindings... however making SPI 
NOR FLASH available as raw MTD device to the OS is sufficiently unusual 
in ACPI systems that there may not be any prior art to follow.


Daniel.


> 
> As you pointed out, are external devices to SOC such exception to use PRP0001 + compatible be it
> i2c slave or SPI slave ?
> 
> 
> Regards
> Udit
> 
>> -----Original Message-----
>> From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
>> Sent: Tuesday, November 21, 2017 7:34 PM
>> To: Udit Kumar <udit.kumar@nxp.com>
>> Cc: Leif Lindholm <leif.lindholm@linaro.org>; edk2-devel@lists.01.org; Varun
>> Sethi <V.Sethi@nxp.com>; Daniel Thompson <daniel.thompson@linaro.org>;
>> Graeme Gregory <graeme.gregory@linaro.org>
>> Subject: Re: [RFC] ACPI table HID/CID allocation
>>
>> On 21 November 2017 at 13:24, Udit Kumar <udit.kumar@nxp.com> wrote:
>>> Thanks Ard,
>>>
>>> My intend of this email to know, what is right way to define HID and
>>> CID in ACPI firmware i.e
>>>
>>> Device(XYZ) {
>>>                  Name(_HID, "NXP0001")
>>>                  Name(_CID, "PRP0001")
>>>            Device(Slave1) {
>>>                                  Name(_CID, "PRP0001")
>>>                   }
>>> }
>>> is ok or
>>>
>>>
>>> Device(XYZ) {
>>>                  Name(_HID, "NXP0001")
>>>                  Name(_CID, " NXP0001")
>>>            Device(Slave1) {
>>>                                  Name(_CID, " NXP0002")
>>>                   }
>>> }
>>> Seems good
>>>
>>
>> I don't think it makes a lot of sense to use the same value for _HID and _CID, so
>> you can just drop the latter.
> 
> Sure,
>   
>>> For sure, AML methods (as needed _ON/OFF/RST/STA etc) /_DSD will to be
>> coded in table using either of.
>>>
>>> Please see more in line
>>>
>>> Regards
>>> Udit
>>>
>>>> -----Original Message-----
>>>> From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
>>>> Sent: Tuesday, November 21, 2017 5:59 PM
>>>> To: Udit Kumar <udit.kumar@nxp.com>
>>>> Cc: Leif Lindholm <leif.lindholm@linaro.org>;
>>>> edk2-devel@lists.01.org; Varun Sethi <V.Sethi@nxp.com>; Daniel
>>>> Thompson <daniel.thompson@linaro.org>; Graeme Gregory
>>>> <graeme.gregory@linaro.org>
>>>> Subject: Re: [RFC] ACPI table HID/CID allocation
>>>>
>>>> On 21 November 2017 at 11:32, Udit Kumar <udit.kumar@nxp.com> wrote:
>>>>>
>>>>>> On 21 November 2017 at 09:59, Udit Kumar <udit.kumar@nxp.com>
>> wrote:
>>>>>>> Thanks Ard.
>>>>>>> Below table was for example. I am not converting whole DT to
>>>>>>> ACPI tables :) My idea is to reduce Linux patches for probing as possible.
>>>>>>> Also keeping firmware and OS separately then Let firmware expose
>>>>>>> both way (HID and PRP00001) and Linux to decide binding
>>>>>>
>>>>>> No.
>>>>>>
>>>>>> You are still assuming ACPI and DT device drivers bind at the same
>>>>>> level, and they don't.
>>>>>
>>>>> No, my above comments was just limited to binding.
>>>>
>>>> Yes, but if you leave it to the OS to decide which binding it uses,
>>>> you will have to support all of them into eternity. And the more
>>>> detailed binding you need to support may limit you in the available
>>>> choices when it comes to making hardware changes, something ACPI allows
>> you to do.
>>>
>>> Thanks,
>>> Is this ok to say , we can provide max same properties in driver as of
>>> DT (with _DSD) , But prefer to use AML methods.
>>> With note, clocking regulators are out of scope here.
>>>
>>
>> Yes. _DSD may be used to describe device specific data that goes beyond what
>> ACPI can express natively. Using _DSD to describe clocks and regulators is an
>> absolute no-go. Putting things like "status" or "dma-coherent" in _DSD
>> properties is absolutely unacceptable as well.
>> But even things like initialization data that the driver programs into the device a
>> single time really do not belong in _DSD. Instead, it should be the firmware that
>> initializes the device, and presents it to the OS in its initialized state.
>>
> 
> Agreed, I never meant something to add in DSD which was prohibited in ACPI spces.
> 
>>>
>>>>> Right, here device driver should know that device is present in
>>>>> system, I see probe function (device-driver binding) is way to know this.
>>>>> Then driver can execute AML methods exposed by firmware.
>>>>>
>>>>
>>>> Yes, declaring the presence of the device is the main purpose of
>>>> describing it both in ACPI and in DT.
>>>>
>>>>>> An ACPI device has AML methods to manage power state and perform
>>>>>> other device related low-level tasks. The device driver has no
>>>>>> knowledge of the hardware beyond what it needs to invoke those
>>>>>> abstract
>>>> methods.
>>>>>
>>>>> You meant, If we need to update driver for AML methods then why not
>>>>> to
>>>> update binding as well . ?
>>>>>
>>>>
>>>> No. What I am saying is that you should not expose two different
>>>> bindings, and let the OS choose.
>>>
>>> Ok, got it , then PRP00001 stuff should be used only at urgent or say
>>> no other choice left , Right ?
>>>
>>
>> Yes.
> 
> 
>>>>> On side track,
>>>>>   With limited search,  I got many each driver is having (acpi_id
>>>>> and of_id), looks, acpi support is added on the top of DT flavored drivers.
>>>>> and therefore acpi tables are following the same.
>>>>> Sorry to say, reference I am looking at (edk2-platform) JunoPkg and
>>>>> VExpressPkg, Has following devices has description similar to Device tree
>>>>>      Device (NET0) {
>>>>>      Device (SREG) {
>>>>>      Device (VIRT) {
>>>>
>>>> These were taken from the ACPI tables for an emulator
>>>>
>>>>>     Device(KMI0) {
>>>>
>>>> I have no clue what kind of device this is
>>>>
>>>>>     Device(ETH0) {
>>>>
>>>> This one uses _DSD as intended, to set device properties in a DT
>>>> compatible fashion, but note that this does *not* include the
>>>> 'compatible' property, nor anything else that ACPI defines itself
>>>> (status, dma-coherent, etc)
>>>
>>> Let me put in simple way,
>>> A simple driver can survive only with _DSD in acpi world.
>>> (clocking/regulators are used as said in UEFI/ACPI)
>>>
>>
>> Why can a simple driver only survive with _DSD? That statement does not make
>> any sense to me.
> 
> Why so, please see below one for example
>   
>>> Copying below from Juno,
>>> Are below kind of tables are acceptable ?
>>>
>>>      Device(ETH0) {
>>>        Name(_HID, "ARMH9118")
>>>        Name(_UID, Zero)
>>>        Name(_CRS, ResourceTemplate() {
>>>                Memory32Fixed(ReadWrite, 0x18000000, 0x1000)
>>>                Interrupt(ResourceConsumer, Level, ActiveHigh, Exclusive) { 192 }
>>>        })
>>>        Name(_DSD, Package() {
>>>                     ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>>>                         Package() {
>>>                                 Package(2) {"phy-mode", "mii"},
>>>                                 Package(2) {"reg-io-width", 4 },
>>>                                 Package(2) {"smsc,irq-active-high",1},
>>>                                 Package(2) {"smsc,irq-push-pull",1}
>>>                        }
>>>        }) // _DSD()
>>>      }
>>>
>>
>> Yes. But please be aware that you should not simply invent your own properties
>> here. The _DSD namespace was intended to be managed, and not free for all
> 
> Agreed, I didn’t meant to add something new, which is not available at present,
> 
>   
>> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.k
>> ernel.org%2Fdoc%2FDocumentation%2Facpi%2FDSD-properties-
>> rules.txt&data=02%7C01%7Cudit.kumar%40nxp.com%7C164c1ff7350a4f6373e
>> e08d530e8b591%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63646
>> 8698397705869&sdata=O78k8r6tcK9fwpuTuQ82ZXGiWkBtLduf4bqrM6D6L1U%
>> 3D&reserved=0
>>
>>>>> Where no AML method is exposed. Then I expect OS driver to manage
>>>>> this
>>>> device.
>>>>> While grepping over few other edk2-platforms.  Looks some of
>>>>> methods are abstracted, not whole device.
>>>>>
>>>>
>>>> So what is your point? Why does this argue in favor of allowing
>>>> PRP0001 + compatible?
>>>
>>> I am seeking your help here to define HID and CID,  please see above
>>> Also for non-NXP devices, how to define HID (if PRP0001 + compatible
>>> not to be used)
>>>
>>
>> This could be a valid reason to use PRP0001 + compatible, for things like I2C
>> slaves that are external to the SoC
> 
> Well,  for internal SOC devices, I am in agreement to use NXP specific HIDs
> But for external devices (for which HID is not available), you suggest to go
> With PRP0001 + compatible
>   
>>>>>> A DT device describes everything in detail, and requires clock and
>>>>>> regulator drivers and other bits and pieces that are tightly
>>>>>> coupled to details of the hardware.
>>>>>>
>>>>>> So now, you have the worst of both worlds:
>>>>>>
>>>>>> - you need to implement all of this in firmware so ACPI can
>>>>>> support it,
>>>>>> - you have to expose the internals to the OS so DT can support it.
>>>>>
>>>>> Yes, for time being or may be longer, DT support needs to be there
>>>>> along with ACPI introduction.
>>>>>
>>>>> Are you suggesting here to abstract whole device details from OS
>>>>> and expose AML methods to be used by device driver.
>>>>> And maintain two drivers instead of fitting DT style driver into ACPI world ?
>>>>>
>>>>
>>>> No. You should update the driver so it can support both ACPI and DT bindings.
>>>> That way, the driver can use the abstractions offered by ACPI when it
>>>> can, and can invoke the clock and regulator frameworks and other low
>>>> level infrastructure only when it needs to.
>>>
>>> Ok, I am align on this, to have one driver which supports both.
>>>
>>>> Let me try to illustrate this a bit better: imagine a NXP customer
>>>> that runs a datacenter that has 10,000 NXP servers, and is using RHEL
>>>> x.y. The business is going well, and at some point, he wants to order another
>> 2,000 servers.
>>>> Unfortunately, the vendor cannot supply the exact same revision of
>>>> the hardware, and the latest revision uses some component that is not
>>>> supported in RHEL x.y.
>>>>
>>>> You now have made your customer very unhappy. He invested in RHEL and
>>>> ACPI based servers precisely to avoid this situation. The cost of
>>>> adding 2,000 servers now includes the cost of upgrading the other
>>>> 10,000 servers to a new OS version or the cost of supporting two
>>>> different OS versions at the same time, for a reason that is not justifiable.
>>>
>>> Do you mean here with PRP0001 HID/CID, we cannot use AML methods.
>>
>> You cannot use the abstractions ACPI provides when using PRP0001 +
>> compatible.
> Oh, thx
>