| Message ID | 20160119163104.GA9469@wunner.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tuesday, January 19, 2016 05:31:04 PM Lukas Wunner wrote: > Hi Rafael, > > On Tue, Jan 19, 2016 at 12:59:13AM +0100, Rafael J. Wysocki wrote: > > On Tuesday, January 19, 2016 12:00:47 AM Lukas Wunner wrote: > > > Hi, > > > > > > On Mon, Jan 18, 2016 at 11:46:18PM +0100, Rafael J. Wysocki wrote: > > > > On Monday, January 18, 2016 11:39:07 PM Lukas Wunner wrote: > > > > [cut] > > > > > > > > > If you want to check if the device ir present at all, you cen use > > > > > > > acpi_device_is_present() introduced recently (although that would need > > > > > > > to be exported if you want to use it from a driver). > > > > > > > > > > > > I meant acpi_dev_present(), sorry about the mistake. > > > > > > > > > > > > I guess we should rename it to acpi_device_found() or something similar > > > > > > to avoid such confusion in the future. > > > > > > > > > > The name was chosen because the PCI equivalent is called pci_dev_present() > > > > > and I assumed that name already stuck in developers' heads, so if they're > > > > > looking for an ACPI presence detection function, that's what they'd look > > > > > for first. > > > > > > > > But "present" in ACPI really means something different. There may be ACPI > > > > device objects in the namespace for devices that are not *actually* present. > > > > > > You mean synthesized devices like LNXSYBUS? > > > Don't think anyone is going to test for the presence of that. > > > > No, I mean real devices, where the corresponding ACPI object has _STA that > > returns 0. > > > > There may be a couple of reasons for that. The device the ACPI object > > corresponds to may not be physically present (eg. it may possible to > > hot-add it) or the device may depend on something else for functionality > > and that thing hasn't been set up yet etc. > > > > The presence of an ACPI device object in the namespace means that the > > platform firmware knows about the device, but it need not mean that > > the device is really there. _STA returns that piece of information. > > Thank you for the clarification, these are very good points. > > The drivers in question use acpi_get_devices() merely to probe for > presence of a device in the namespace. They do not invoke _STA, > nor do they even hold a pointer to the acpi_device or acpi_handle > when detecting presence. Mostly this is about activating quirks > if a certain ACPI device is detected. I know, but it doesn't matter too much. I don't want people to wonder what the difference between acpi_dev_present() and acpi_device_is_present() is and when to use which of them. > Currently about 50% of the calls to acpi_get_devices() in the drivers > fit this pattern and the point of acpi_dev_present() is to give > developers a simple, lightweight tool as an alternative. Again, I know, but the name of the function should be different. > However the kernel-doc should be amended to clarify that _STA is not > invoked. The patch below is a suggestion, feel free to rephrase. That's OK, but it's not enough. I guess it won't be a big deal to change the function name and rebase the patches depending on it on top of that change, will it? Thanks, Rafael
diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c index f2f9873..99af3bc 100644 --- a/drivers/acpi/utils.c +++ b/drivers/acpi/utils.c @@ -716,6 +716,8 @@ EXPORT_SYMBOL(acpi_check_dsm); * * Return %true if the device was present at the moment of invocation. * Note that if the device is pluggable, it may since have disappeared. + * Also, this merely checks presence in the namespace but does not + * invoke the _STA control method. * * For this function to work, acpi_bus_scan() must have been executed * which happens in the subsys_initcall() subsection. Hence, do not