From mboxrd@z Thu Jan 1 00:00:00 1970 From: mjg59@srcf.ucam.org (Matthew Garrett) Date: Mon, 25 Nov 2013 15:41:10 +0000 Subject: ACPI In-Reply-To: References: Message-ID: <20131125154110.GB3243@srcf.ucam.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Nov 25, 2013 at 11:33:56AM +0000, Grant Likely wrote: > What I'm assuming here is that on ACPI the pinctrl setup and > management would be performed by the platform in AML methods so that > the kernel isn't aware of them at all. All it know is that it has a > (for example) SPI bus and as far as it is concerned the pins are > correctly attached when the SPI bus is active. My understanding is > that historically this is how ACPI has been used. Pretty much. In the past ACPI implementations handled GPIO by providing methods that accessed hardware registers directly. I've seen DSDTs that implement i2c entirely in ASL. It's *very* common for hwmon devices to be hidden away behind some ACPI methods. The obvious downside of this approach is that there's no real mechanism for allowing a real driver to access the hardware at the same time as the ACPI code, and as a consequence you're limited to whatever functionality is provided by the ACPI code. -- Matthew Garrett | mjg59 at srcf.ucam.org