Hi, > From: Guenter Roeck [mailto:linux@xxxxxxxxxxxx] > Subject: Re: [PATCH] ACPICA: Export mutex functions > > 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@xxxxxxxxxxxx] > >>> Subject: Re: [PATCH] ACPICA: Export mutex functions > >>> > >>> On 04/17/2017 04:53 PM, Zheng, Lv wrote: > >>>> Hi, > >>>> > >>>>> From: Guenter Roeck [mailto:linux@xxxxxxxxxxxx] > >>>>> 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@xxxxxxxxxxxx> wrote: > >>>>>>> On Mon, Apr 17, 2017 at 08:40:38PM +0000, Moore, Robert wrote: > >>>>>>>> > >>>>>>>> > >>>>>>>>> From: Guenter Roeck [mailto:linux@xxxxxxxxxxxx] > >>>>>>>>> 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. >From the above AML code, the solution 2 is not possible for ensuring the mutual exclusion of accessing the resources. Because the mutual exclusion must be ensured for the entire transaction including ENFG() and EXFG() rather than a single SystemIo operation region field access. So you really need the solution 1 and the new API. Thanks and best regards Lv > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
