RE: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmuxmappings

[Dong Aisheng-B29396]

> -----Original Message-----
> From: Stephen Warren [mailto:swarren@xxxxxxxxxx]
> Sent: Thursday, January 12, 2012 4:18 AM
> To: Dong Aisheng-B29396; Dong Aisheng
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linus.walleij@xxxxxxxxxxxxxx;
> s.hauer@xxxxxxxxxxxxxx; rob.herring@xxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx; cjb@xxxxxxxxxx; devicetree-
> discuss@xxxxxxxxxxxxxxxx; Simon Glass (sjg@xxxxxxxxxxxx)
> Subject: RE: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux
> mappings
> Importance: High
> 
> Dong Aisheng wrote at Tuesday, January 10, 2012 1:21 AM:
> > Stephen Warren wrote at Saturday, January 07, 2012 2:03 AM:
> ...
> > > Now in the board's .dts file, you need to specify for each device
> > > the list of pinmux groups the device needs to use, and the function to
> select for each group.
> > > Perhaps something like:
> > >
> > > board.dts:
> > >
> > > usdhc@0219c000 { /* uSDHC4 */
> > >         fsl,card-wired;
> > >         status = "okay";
> > >         pinmux = <&foogrp &uart3func &bazgrp &uart4func>; };
> > >
> > > I haven't convinced myself that's actually a good binding, but I
> > > think it does represent the data required for muxing. Some potential issues
> as before:
> >
> > Here is what we should discuss exactly.
> > Since 'pinmux' phandle will be parsed in pinctrl core, we should try
> > to find and define a common and standardized pinmux property for all platforms.
> 
> Yes.
> 
> ...
> > To keep consistency as the currently design of pinctrl subsystem and
> > also meet the dt design philosophy, we still do not introduce a pinmux map in
> dt.
> > Instead, we choose to scan all the device node with a 'pinmux' phandle
> > to construct a pinmux map table before register the pin controller
> > device(here we may also scan the hog_on_boot node) and I guess it's easy to do
> that.
> ...
> > (Without scan the device node to construct the pinmux map table, we
> > can only get the map Information when we run the pinmux_get.
> > See: https://lkml.org/lkml/2012/1/5/153
> > So no pinmux map table exists and we surely do not want to see that
> > the sysfs exporting pinmux map information works in dt but unwork in
> > non-dt)
> 
> Hmmm. I'm not sure that the pinctrl code should actively scan all nodes in the
> device tree for pin mux properties. That seems a little invasive; how does
It's one solution although not good.

> pinctrl know which nodes it really should be looking at, and which nodes are
> random internal parts of some device's custom binding?
> 
Looking at all device nodes with 'pinmux' property which should not be used by
Others.

> Personally, I think I'd be OK with the sysfs pinctrl map file only containing
> the map entries for devices that had used the pinctrl API, and hence only
> parsing the pinmux properties in pinmux_get().
> 
Actually I already did it like that in the patch I sent:
https://lkml.org/lkml/2012/1/5/153

Originally I'd like to do like that but I found an inconsistent issue that
the sysfs pinctrl map file will behave differently between dt and non-dt
Platform. For non-dt, it means showing all exist map entries. For dt, it means
Only used pinmux map entries.

And in current design when device calls pinmux_get, it will search a predefined
pinmux_maps array to find which function and group it is binded to.
If switch to the new way, we only dynamically create pinmux map and dynamically 
register it when pinmux_get is called, first we need to change the code path in
pinmux_get in a totally different way, second for support that we may also better
to change pinmux_maps array to a list.
But after changing the pinmux_maps to a list, what about using in non-dt?

So without any strong reason i still think it would be better to keep consistency
With the non-dt pinctrl subsystem.
And the effort would be minimum since besides constructing the map by parsing
Device tree, everyting is the same as before in pinmux map and we could re-use
the current code.

> However, we could perhaps do better by registering a bus notifier, and pro-
> actively parsing the top-level DT node (if there is one) for every device that
> is created. That way, the mapping would be parsed as soon as the device was
> created (or perhaps after probe?). The only case this might not cover is DT
> nodes for which the kernel doesn't actually have a driver, and hence no device
> is created.
> 
> > BTW it seems you want to support multi pin groups(foogrp and bazgrp)
> > for one device, do we have such using case?
> > I guess usually one pin group already contains all the pins of device.
> > Anyway, just from flexibility view, it's good for me.
> 
> Yes.
> 
> Recall that I believe that pin group definitions should only exist where the HW
> itself muxes pins on a per-group basis rather than a per-pin basis.
> This may be a bit different to what you mean by a group. Anyway...
> 
> As an example on Tegra, we have:
> 
> * SD controller 4 HW block
> * Pin group ATB contains two pins, which are the CLK and CMD signals
>   when the SDIO4 function is muxed onto the group.
> * Pin group GMA contains four pins, which are DATA[3:0] when the SDIO4
>   function is muxed onto the group.
> * Pin group GME contains four pins, which are DATA[7:4] when the SDIO4
>   function is muxed onto the group.
> 
> Hence, a board that uses this SD controller in that configuration would need 3
> entries in its pinmux property/node.
> 
Unsertood.

> In general, I think all SoCs are likely to be the same way, except that you'd
> need n pins in the list instead of n groups, again recalling that I'm talking
> about HW-level pins/groups, not entries in a "supported configuration" list.
> 
> --
> nvpublic
> 

Regards
Dong Aisheng

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