On Wed, Jan 24, 2018 at 3:29 PM, Sinan Kaya <okaya@xxxxxxxxxxxxxx> wrote: > +linux-acpi +Cc: Hans > On 1/24/2018 1:27 AM, Mika Westerberg wrote: >> On Wed, Jan 24, 2018 at 06:56:16AM +0100, Wolfram Sang wrote: >>> On Wed, Jan 03, 2018 at 03:02:31PM +0100, Eric Auger wrote: >>>> If I2C is built as a module, ACPI_I2C_OPREGION cannot be set >>>> and any ACPI opregion calls targeting I2C fail with no opregion found. >>>> >>>> This patch allows ACPI_I2C_OPREGION to be enabled both if I2C is >>>> built into the kernel or built as a module. >>>> >>>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx> >>> >>> I recall that we had some discussion until ending up with the current >>> solution. And I finally found it again: >>> >>> http://www.serverphorums.com/read.php?12,1001402 >>> >>> In any case, I surely want Mika's ack on any change to ACPI related >>> Kconfig symbols. Adding him to CC... >> >> So the problem is/was that what happens if you are in a middle of BIOS >> AML code touching the opregion and someone unloads the opregion handler? >> If you can quarantee nothing bad happens, then I'm fine with the patch :) >> > > Rafael to correct me if I got this right. > > The behavior of the operating system is well defined in the ACPI specification. > > Here is what I tested recently: > > ACPI defines _REG method to inform firmware of presence/removal of an operating > region. > > When driver gets loaded, ACPI calls the _REG method with 1 argument. When driver > gets unloaded, ACPI call the _REG method with 0 argument. > > Firmware can use this notification to its advantage to determine when an I2C > related functionality should be accessed or not. > > If firmware doesn't use the _REG method, ACPI defines that AML statements > accessing the operating region are ignored. > > You'll also see a warning from ACPICA saying the OperatingRegion 9 is no longer > accessible and AML code execution failed. > > Also note that someone can always unbind an I2C driver from ACPI even with built-in > module. No, you can't. There are user(s) of that, i.e. PMIC, otherwise, of course, you may do that. > I think we are talking about an orthogonal issue here. -- With Best Regards, Andy Shevchenko
