linux-kernel - Re: [PATCH 3/7] pinctrl: pinconf-generic: Allow driver to specify DT params

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Date:	Thu, 20 Nov 2014 10:06:17 +0200
From:	"Ivan T. Ivanov" <iivanov@...sol.com>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Bjorn Andersson <Bjorn.Andersson@...ymobile.com>,
	Michal Simek <michal.simek@...inx.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Alessandro Rubini <rubini@...pv.it>,
	Heiko Stuebner <heiko@...ech.de>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-rockchip@...ts.infradead.org,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>
Subject: Re: [PATCH 3/7] pinctrl: pinconf-generic: Allow driver to specify
 DT params


On Wed, 2014-11-19 at 07:35 -0800, Sören Brinkmann wrote:
> Hi Ivan,
> 
> On Wed, 2014-11-19 at 09:49AM +0200, Ivan T. Ivanov wrote:
> > On Tue, 2014-11-18 at 09:25 -0800, Sören Brinkmann wrote:
> > > On Tue, 2014-11-18 at 10:50AM +0200, Ivan T. Ivanov wrote:
> > > > On Tue, 2014-11-11 at 15:53 +0100, Linus Walleij wrote:
> > > > > On Mon, Nov 3, 2014 at 8:05 PM, Soren Brinkmann
> > > > > brinkmann@...inx.com> wrote:
> > > > > 
> > > > > > Additionally to the generic DT parameters, allow drivers to
> > > > > > provide driver-specific DT parameters to be used with the
> > > > > > generic parser infrastructure.
> > > > > > 
> > > > > > Signed-off-by: Soren Brinkmann brinkmann@...inx.com>
> > > > > 
> > > > > I like the looks of this, but the patch description is a bit
> > > > > terse. I'd like it to describe some of the refactorings being
> > > > > done
> > > > > to the intrinsics, because I have a hard time following the
> > > > > patch.
> > > > > 
> > > > > First please rebase onto the "devel" branch in the pin control
> > > > > tree, and notice that drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
> > > > > which is merged there is actually doing this already:
> > > > > 
> > > > > 
> > > > >         for_each_child_of_node(np_config, np) {
> > > > >                 ret = pinconf_generic_dt_subnode_to_map(pctldev,
> > > > > np, map,
> > > > >                                                         &reserv,
> > > > > nmaps, type);
> > > > >                 if (ret)
> > > > >                         break;
> > > > > 
> > > > >                 ret = pmic_gpio_dt_subnode_to_map(pctldev, np,
> > > > > map, &reserv,
> > > > >                                                   nmaps, type);
> > > > >                 if (ret)
> > > > >                         break;
> > > > >         }
> > > > > 
> > > > > So it should be patched to illustrate the point of this code.
> > > > > 
> > > > 
> > > > I like the idea, but have issues with implementations :-).
> > > > 
> > > > It is supposed that additional parameters are not generic,
> > > > otherwise they will be part of enum pin_config_param, right?
> > > > 
> > > > Probably it will be better if clients could pass array with
> > > > driver specific dt bindings to pinconf_generic_dt_node_to_map()?
> > > 
> > > My idea was to hide that API from the driver. You just pass those
> > > parameters as part of the struct pctldev and the parser - whether
> > > this generic one or anything else - would do the right thing. I
> > > don't think calling the parser from the driver is the right approach.
> > 
> > Drivers already know about dt_node_to_map(). My proposal will make
> > drivers, which register non-standard bindings, little bit simpler.
> 
> And I think this is not the best solution. Those drivers essentially
> still do the DT parsing themselves, 

Yes, and this could be avoided if there API which allow them to pass 
non-standard configuration maps.

> just call some common helpers. I
> think that should be well separated. 

Around 27 of 30 drivers are using custom dt_node_to_map(). And this is
because most of them are using custom "x,pins", "x,functions" and 'x,groups"
properties and I think that this is bigger issue, how this is addressed
in this patch?

> The pinctrl driver just assembles
> some data structure that has the information regarding custom properties
> and the core handles the rest. 

Yup, that is nice. What will be really nice if it also handle custom, 
"function", "groups" and "pins" properties. Otherwise most of the drivers
will not be able to benefit from this. 

I just wanted to share my opinion.

Regards,
Ivan

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