From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Date: Mon, 30 Jul 2012 22:26:28 +0000 Subject: Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences Message-Id: <50170A14.6000201@wwwdotorg.org> List-Id: References: <1343390750-3642-1-git-send-email-acourbot@nvidia.com> <1343390750-3642-2-git-send-email-acourbot@nvidia.com> <5016ABDD.5010809@gmail.com> In-Reply-To: <5016ABDD.5010809-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Rob Herring Cc: Alexandre Courbot , Stephen Warren , Thierry Reding , Simon Glass , Grant Likely , Greg Kroah-Hartman , Mark Brown , Arnd Bergmann , linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fbdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org On 07/30/2012 09:44 AM, Rob Herring wrote: > On 07/27/2012 07:05 AM, Alexandre Courbot wrote: >> Some device drivers (panel backlights especially) need to follow precise >> sequences for powering on and off, involving gpios, regulators, PWMs >> with a precise powering order and delays to respect between each steps. >> These sequences are board-specific, and do not belong to a particular >> driver - therefore they have been performed by board-specific hook >> functions to far. >> >> With the advent of the device tree and of ARM kernels that are not >> board-tied, we cannot rely on these board-specific hooks anymore but >> need a way to implement these sequences in a portable manner. This patch >> introduces a simple interpreter that can execute such power sequences >> encoded either as platform data or within the device tree. >> > > Why not? We'll always have some amount of board code. The key is to > limit parts that are just data. I'm not sure this is something that > should be in devicetree. > > Perhaps what is needed is a better way to hook into the driver like > notifiers? I would answer that by asking the reverse question - why should we have to put some data in DT, and some data into board files still? I'd certainly argue that the sequence of which GPIOs/regulators/PWMs to manipulate is just data. To be honest, if we're going to have to put some parts of a board's configuration into board files anyway, then the entirety of DT seems useless; I'd far rather see all the configuration in one cohesive place than arbitrarily split into two/n different locations - that would make everything harder to maintain.