+linux-acpi 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. I think we are talking about an orthogonal issue here. -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project. -- 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
