lkml.org 
[lkml]   [2012]   [Jan]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Pinmux bindings proposal V2
* Shawn Guo <shawn.guo@linaro.org> [120129 17:13]:
> On Fri, Jan 27, 2012 at 09:05:45AM -0800, Tony Lindgren wrote:
> > Hi,
> >
> > * Shawn Guo <shawn.guo@linaro.org> [120126 22:15]:
> > > On Thu, Jan 26, 2012 at 06:08:33PM -0800, Tony Lindgren wrote:
> > > > * Stephen Warren <swarren@nvidia.com> [120126 11:03]:
> > > ...
> > > > > Second, as I mentioned before, while some of the states are certainly
> > > > > PM-related, I don't think all will be, e.g. the case of running an SD
> > > > > controller at different clock rates to the SD card, and needing to
> > > > > set different pin parameters based on the clock rate. Is runtime PM
> > > > > intended cover that kind of thing? The idea here is that the common
> > > > > pinctrl binding can allow the driver to require different named states
> > > > > for those different clock rate cases.
> > > >
> > > > For the PM related states, those should be Linux generic. For rate
> > > > setting sounds like that's really something you should set up as clocks
> > > > in the Tegra wrapper driver for SDHCI?
> > > >
> > > That's right.
> > >
> > > > Ideally the SDHCI driver would be completely arch independent, and
> > > > then the SoC specific wrapper driver would know how to communicate to
> > > > the pinmux/pinconf framwork or clock framework what it needs using
> > > > Linux generic APIs.
> > >
> > > But that wrapper driver should not be bothered to call pinmux/pinconf
> > > APIs on pin basis to change the pinctrl configuration. The elegant
> > > way would be something like the following in case that it switches
> > > the bus frequency from 50 MHz to 100 MHz.
> > >
> > > pmx = pinmux_get(dev, "esdhc_50mhz");
> > > ...
> > > pinmux_put(pmx);
> > > pmx = pinmux_get(dev, "esdhc_100mhz");
> > > ...
> > >
> > > The specific mux and config settings of states esdhc_50mhz and
> > > esdhc_100mhz would be retrieved from device tree.
> >
> > Yes whatever mux names can be used, same as with clock framework
> > for clock names. But that means you'll have to constantly get/put
> > the mux which is not efficient.
> >
> The most important reason that we want to move to pinctrl subsystem
> is we need its run-time configuration feature for cases like esdhc
> here. I do not think the switch here is so constant to be inefficient.
>
> > Wouldn't it be cleaner to just clk_get esdhc_clk during init, then
> > do clk_set_rate on it to toggle the rates?
> >
> It's not an init-time switch but run-time one. That said,
> sdhci_ops.set_clock will be called during run-time.

Right, basically you don't want to do clk_get or pinmux_get during
runtime, you do that once one during init. Then do clk_set_rate or
whaterver during runtime.

Is there anything stopping from implementing sdhci_ops.set_rate
using clock framework and clk_set_rate in this case BTW?

> > > > So I'd rather stay out of random named states for
> > > > the pins coming from device tree; If we still need them, they should
> > > > be common bindings rather than things like "xyz_clock_hack".
> > > >
> > > The binding defines the syntax, and I do not see the necessity to
> > > force the particular state name, which is really pinctrl client
> > > device specific.
> >
> > Do you have some other custom pin state example other than the
> > clock rate change example above?
> >
> I have another case PM related. To aggressively save power, the pins
> configured for particular function during active mode need to be
> muxed on gpio mode and output 0 in low-power mode.

OK, but basically only a small subset of pins of the total pins?

Regards,

Tony


\
 
 \ /
  Last update: 2012-01-30 18:23    [W:0.083 / U:12.556 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site