Messages in this thread | | | Subject | Re: [PATCH] ACPICA: Export mutex functions | From | Guenter Roeck <> | Date | Tue, 18 Apr 2017 06:50:26 -0700 |
| |
On 04/18/2017 12:14 AM, Zheng, Lv wrote: > Hi, > >> From: Zheng, Lv >> Subject: RE: [PATCH] ACPICA: Export mutex functions >> >> Hi, >> >>> From: Guenter Roeck [mailto:linux@roeck-us.net] >>> Subject: Re: [PATCH] ACPICA: Export mutex functions >>> >>> On 04/17/2017 04:53 PM, Zheng, Lv wrote: >>>> Hi, >>>> >>>>> From: Guenter Roeck [mailto:linux@roeck-us.net] >>>>> Subject: Re: [PATCH] ACPICA: Export mutex functions >>>>> >>>>> On Mon, Apr 17, 2017 at 11:29:38PM +0200, Rafael J. Wysocki wrote: >>>>>> On Mon, Apr 17, 2017 at 11:03 PM, Guenter Roeck <linux@roeck-us.net> wrote: >>>>>>> On Mon, Apr 17, 2017 at 08:40:38PM +0000, Moore, Robert wrote: >>>>>>>> >>>>>>>> >>>>>>>>> From: Guenter Roeck [mailto:linux@roeck-us.net] >>>>>>>>> Subject: Re: [PATCH] ACPICA: Export mutex functions >>>>>>>>> >>>>>>>>> On Mon, Apr 17, 2017 at 07:27:37PM +0000, Moore, Robert wrote: >>>>>>>>>> >>>>>>>>>>> From: Moore, Robert >>>>>>>>>>> Subject: RE: [PATCH] ACPICA: Export mutex functions >>>>>>>>>>> >>>>>>>>>>> There is a model for the drivers to directly acquire an AML mutex >>>>>>>>>>> object. That is why the acquire/release public interfaces were added >>>>>>>>>>> to ACPICA. >>>>>>>>>>> >>>>>>>>>>> I forget all of the details, but the model was developed with MS and >>>>>>>>>>> others during the ACPI 6.0 timeframe. >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> [Moore, Robert] >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> Here is the case where the OS may need to directly acquire an AML >>>>>>>>> mutex: >>>>>>>>>> >>>>>>>>>> From the ACPI spec: >>>>>>>>>> >>>>>>>>>> 19.6.2 Acquire (Acquire a Mutex) >>>>>>>>>> >>>>>>>>>> Note: For Mutex objects referenced by a _DLM object, the host OS may >>>>>>>>> also contend for ownership. >>>>>>>>>> >>>>>>>>> From the context in the dsdt, and from description of expected use cases >>>>>>>>> for _DLM objects I can find, this is what the mutex is used for (to >>>>>>>>> serialize access to a resource on a low pin count serial interconnect, >>>>>>>>> aka LPC). >>>>>>>>> >>>>>>>>> What does that mean in practice ? That I am not supposed to use it >>>>>>>>> because it doesn't follow standard ACPI mutex declaration rules ? >>>>>>>>> >>>>>>>>> Thanks, >>>>>>>>> Guenter >>>>>>>>> >>>>>>>>>> >>>>>>>> [Moore, Robert] >>>>>>>> >>>>>>>> I'm not an expert on the _DLM method, but I would point you to the description section in the >>>>> ACPI spec, 5.7.5 _DLM (DeviceLock Mutex). >>>>>>>> >>>>>>> >>>>>>> I did. However, not being an ACPI expert, that doesn't tell me anything. >>>>>> >>>>>> Basically, if the kernel and AML need to access a device concurrently, >>>>>> there should be a _DLM object under that device in the ACPI tables. >>>>>> In that case it is expected to return a list of (AML) mutexes that can >>>>>> be acquired by the kernel in order to synchronize device access with >>>>>> respect to AML (and for each mutex it may also return a description of >>>>>> the specific resources to be protected by it). >>>>>> >>>>>> Bottom line: without _DLM, the kernel cannot synchronize things with >>>>>> respect to AML properly, because it has no information how to do that >>>>>> then. >>>>> >>>>> That is all quite interesting. I do see the mutex in question used on various >>>>> motherboards from various vendors (I checked boards from Gigabyte, MSI, and >>>>> Intel). Interestingly, the naming seems to be consistent - it is always named >>>>> "MUT0". For the most part, it seems to be available on more recent >>>>> motherboards; older motherboards tend to use the resource without locking. >>>>> However, I don't see any mention of "_DLM" in any of the DSDTs. >>>>> >>>> >>>> OK, then you might be having problems in your opregion driver. >>>> >>>>> At the same time, access to ports 0x2e/0x2f is widely used in the kernel. >>>>> As mentioned before, it is used in watchdog, hardware monitoring, and gpio >>>>> drivers, but also in parallel port and infrared driver code. Effectively >>>>> that means that all this code is inherently unsafe on systems with ACPI >>>>> support. >>>>> >>>>> I had thought about implementing a set of utility functions to make the kernel >>>>> code safer to use if the mutex is found to exist. >>>> >>>> As what you've mentioned, there are already lots of parallel accesses in kernel without enabling >>> ACPI. >>>> Are these accesses mutually exclusive (safe)? >>> >>> In-kernel, yes (using request_muxed_region). Against ACPI, no. >>> >>>> If so, why do you need to invent a new synchronization mechanism? >>>> >>> >>> Because I am seeing a problem with the current code (more specifically, >>> with the it87 hwmon driver) on new Gigabyte boards. >> >> I checked superio_enter()/superio_exit(), IMO, the mutual exclusion >> might be handled using 1 of the following 2 solutions: >> >> 1. _DLM, then you can find superio related mutex from _DLM and >> acquire/release it in superio_enter()/superio_exit(). >> You really need a set of new APIs to acquire the _DLM related mutex. >> If you don't have _DLM in your DSDT, directly exporting ACPICA mutex >> functions seem to be a reasonable solution. >> 2. Normally, AML developer should abstract superio accesses into customized >> opregion, then you can prepare a superio opregion driver. >> >>> >>>>> Right now I wonder, though, >>>>> if such code would have a chance to be accepted. Any thoughts on that ? >>>> >>>> Is that possible to make it safe in the opregion driver? >>>> >>> >>> Sorry, I don't think I understand what you mean with "opregion driver". >>> Do you refer to the drivers accessing the memory region in question, >>> or in other words replicating the necessary code in every driver accessing >>> that region ? Sure, I can do that, if that is the preferred solution; >>> I have no problem with that. However, that would require exporting >>> the ACPI mutex functions. My understanding is that you are opposed to >>> exporting those, so I assume that is not what you refer to. >>> Can you clarify ? >> >> I mean solution 2. > > Maybe I should provide more detailed examples for this solution. > > For example: > OperationRegion (SIOT, SuperIOAddressSpace, Zero, 100) > Field (SIOT, ByteAcc, Lock, Preserve) > { > FNC1, 8, > FNC2, 8, > ... > } > > Acquire (MUX0) > Store (0, FNC1) > Release (MUX0) > > Then you can call (let me use casual pseudo code) > acpi_install_operation_region(SuperIOAddressSpace, superio_opregion_handler) from OS side. > In its callback superio_opregion_handler(), you can: > > superio_enter(); > If (address == 0) { > /* mean FNC1 */ > Perform the locked superior accesses > } else if (address == 1) { > /* mean FNC2 */ > Perform the locked superior accesses > } > superio_exit(); > > Are there similar approach in your DSDT? >
Some snippets from the DSDT:
Device (SIO1) { Name (_HID, EisaId ("PNP0C02") /* PNP Motherboard Resources */) // _HID: Hardware ID Name (_UID, Zero) // _UID: Unique ID ... Mutex (MUT0, 0x00) Method (ENFG, 1, NotSerialized) { Acquire (MUT0, 0x0FFF) INDX = 0x87 INDX = One INDX = 0x55 If ((SP1O == 0x2E)) { INDX = 0x55 } Else { INDX = 0xAA }
LDN = Arg0 }
Method (EXFG, 0, NotSerialized) { INDX = 0x02 DATA = 0x02 Release (MUT0) }
OperationRegion (IOID, SystemIO, SP1O, 0x02) /* SP1O is 0x2e */ Field (IOID, ByteAcc, NoLock, Preserve) { INDX, 8, DATA, 8 } ...
Example for use: Method (DCNT, 2, NotSerialized) { ENFG (CGLD (Arg0)) If (((DMCH < 0x04) && ((Local1 = (DMCH & 0x03)) != Zero))) { RDMA (Arg0, Arg1, Local1++) }
ACTR = Arg1 Local1 = (IOAH << 0x08) Local1 |= IOAL RRIO (Arg0, Arg1, Local1, 0x08) EXFG () }
Can there be more than one address space handler for a given region ? Each driver accessing the resource would need that handler.
Thanks, Guenter
> Thanks and best regards > Lv > >> From it87_find() I really couldn't see a possibility to convert superio >> accesses into opregions. Could you paste some example superio access AML >> code from your DSDT here. >> >> Thanks and best regards >> Lv >
| |