From mboxrd@z Thu Jan 1 00:00:00 1970 From: robh+dt@kernel.org (Rob Herring) Date: Fri, 11 Dec 2015 08:06:22 -0600 Subject: [PATCH 1/3] Device tree binding documentation for gpio-switch In-Reply-To: References: <1449250275-23435-1-git-send-email-martyn.welch@collabora.co.uk> <1449250275-23435-2-git-send-email-martyn.welch@collabora.co.uk> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Dec 11, 2015 at 6:39 AM, Linus Walleij wrote: > On Fri, Dec 4, 2015 at 6:31 PM, Martyn Welch > wrote: > >> This patch adds documentation for the gpio-switch binding. This binding >> provides a mechanism to bind named links to gpio, with the primary >> purpose of enabling standardised access to switches that might be standard >> across a group of devices but implemented differently on each device. >> >> Signed-off-by: Martyn Welch > > As mentioned in the comment to the second patch, this solves the > following generic problem: > > Expose a GPIO line to userspace using a specific name > > That means basically naming GPIO lines and marking them as > "not used by the operating system". > > This is something that has been proposed before, and postponed > because the kernel lacks the right infrastructure. That doesn't necessarily mean we can't define a binding. > Markus Pargmann also did a series that add initial values to > hogs, which is the inverse usecase of this, where you want to > *output* something by default, then maybe also make it available > to userspace. > > So what we need to see here is a patch series that does all of these > things: > > - Name lines > > - Sets them to initial values > > - Mark them as read-only > > - Mark them as "not used by the operating system" so that they > can be default-exported to userspace. No! This should not be a DT property. Whether I want to control a GPIO in the kernel or userspace is not known and can change over time. It could simply depend on kernel config. There is also the case that a GPIO has no connection or kernel driver until some time later when a DT overlay for an expansion board is applied. Rob