From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Courbot Date: Tue, 31 Jul 2012 10:15:57 +0000 Subject: Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences Message-Id: <5017B05D.9020506@nvidia.com> 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> <50170A14.6000201@wwwdotorg.org> In-Reply-To: <50170A14.6000201-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Stephen Warren Cc: Rob Herring , 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 07/31/2012 07:26 AM, Stephen Warren wrote: > 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. Also, having these sequences into the DT would allow an older kernel to boot on and correctly initialize a newer board with - which is also part of the DT's purpose if I am not mistaken. Alex.