[PATCH 3/4] OMAPDSS: panel-sharp-ls037v7dw01: add device tree support

Javier Martinez Canillas javier at dowhile0.org
Mon May 12 02:34:07 PDT 2014

Hello Tomi,

On Mon, May 12, 2014 at 9:38 AM, Tomi Valkeinen <tomi.valkeinen at ti.com> wrote:
> On 09/05/14 18:55, Tony Lindgren wrote:
>>> Although if the MO gpio is not controlled by the driver, we should tell
>>> the driver whether that gpio is high or low.
>> What do you have in mind for telling that? We should also tell the
>> orientation of the panel:
>> EVM   VGA     omapfb.rotate=3
>> LDP   QVGA    omapfb.rotate=0
>> Do you have something in mind for that?
> Hmm, right. I guess all we can do is have boolean flags in the .dts for
> MO, LR and UD, which tells if the respective pins are hard-wires high or
> low. And say in the documentation that you must either have a proper
> GPIO, or use the flag, but not both.
> The panel mounting orientation is a different matter. But I think it is
> also something we should specify in the .dts. However, we don't have any
> SW support to handle it, and it's a bit unclear to me how it should be
> handled, so I think that has to be left for later.
>>> At the moment our display drivers are OMAP specific, and for that reason
>>> we should prefix the compatible strings with "omapdss,". For example,
>>> drivers/video/fbdev/omap2/displays-new/panel-dsi-cm.c:
>>>      { .compatible = "omapdss,panel-dsi-cm", },
>>> But we should still have the right compatible string in the .dts, so we
>>> convert the compatible name in arch/arm/mach-omap2/display.c, with
>>> 'dss_compat_conv_list' array, to which this panel's name should be added.
>> Oh so what do you want to have in the .dts file then?
> The .dts should have the proper names. The idea of this hackery is that
> in the .dts we can have the proper compatible string. So in the .dts, we
> have, say:
> "sony,panel-foobar"
> Then, at boot time, omap's platform code changes that to:
> "omapdss,sony,panel-foobar".
> And our (omap specific) panel-foobar driver use that
> "omapdss,sony,panel-foobar" string.
> This way some other platform could do the same, and have their platform
> specific drivers handle the panel.
> At some point in the future we hopefully will have common panel drivers,
> and at that point we can remove that hackery. The .dts files will
> already be correct.

Maybe we can remove this hackery by relying on the fact that a
compatible string can have a set of values that goes from more
specific to more general. So you can have something like:

compatible = "sony,panel-foobar", "omapdss,panel-foobar"

So right now only "omapdss,panel-foobar" will be matched and later
when we have common panel drivers then that driver could handle the
"sony,panel-foobar" compatible string.

Other platforms could do something similar and have

compatible = "sony,panel-foobar", "baz,panel-foobar"

That way you won't break DT backward compatible but still not require
hacks on arch/arm/mach-omap2/display.c.

We do the same for OMAP boards, we now have the following compatible string:

compatible = "isee,omap3-igep0020", "ti,omap36xx", "ti,omap3";

There isn't a struct machine_desc that matches "isee,omap3-igep0020"
but later if we find that we need some board specific initialization
we could add one without breaking existing DTS. In fact it used to be
a single machine_desc that matched "ti,omap3" for both omap36xx and
omap34xx but later when some DT clocks changes were introduced we
needed to split both SoC families.

>  Tomi

Best regards,

More information about the linux-arm-kernel mailing list