Re: [PATCH 3/3] watchdog: omap_wdt: add device tree support

[Cousson, Benoit]

Hi Jon,

On 5/30/2012 5:03 PM, Jon Hunter wrote:
> Hi Benoit,
>
> On 05/30/2012 02:54 AM, Cousson, Benoit wrote:
> > On 5/30/2012 5:18 AM, Xiao Jiang wrote:
> > > Jon Hunter wrote:
> > > > On 05/25/2012 05:42 AM, jgq516@xxxxxxxxx wrote:
> > > > > From: Xiao Jiang<jgq516@xxxxxxxxx>
> > > > >
> > > > > Add device table for omap_wdt to support dt.
> > > > >
> > > > > Signed-off-by: Xiao Jiang<jgq516@xxxxxxxxx>
> > > > > ---
> > > > > drivers/watchdog/omap_wdt.c | 8 ++++++++
> > > > > 1 files changed, 8 insertions(+), 0 deletions(-)
> > > > >
> > > > > diff --git a/drivers/watchdog/omap_wdt.c b/drivers/watchdog/omap_wdt.c
> > > > > index 8285d65..d98c615 100644
> > > > > --- a/drivers/watchdog/omap_wdt.c
> > > > > +++ b/drivers/watchdog/omap_wdt.c
> > > > > @@ -430,6 +430,13 @@ static int omap_wdt_resume(struct
> > > > > platform_device *pdev)
> > > > > #define omap_wdt_resume NULL
> > > > > #endif
> > > > >
> > > > > +static const struct of_device_id omap_wdt_of_match[] = {
> > > > > + { .compatible = "ti,omap3-wdt", },
> > > > > + { .compatible = "ti,omap4-wdt", },
> >
> > If there is no difference between the OMAP3 and the OMAP4 WDT IP, just
> > add one entry "ti,omap3-wdt". And then in the OMAP4 DTS you will just
> > put : compatible = "ti,omap3-wdt"; or compatible =  "ti,omap4-wdt",
> > "ti,omap3-wdt";
>
> Hmmm ... comparing the omap3 and omap4 wdt registers there are some
> differences. omap4 seems to have more registers than omap3. May be we
> are not using these right now, but from a register perspective the wdt
> in omap2, omap3 and omap4 appear to be slightly different. The revision
> ID register on omap3 and omap4 have different values too.
>
> I guess from a driver perspective there is no difference, but it seemed
> to me that the IP is not completely the same.

Well, in that case, and assuming that there is no proper HW_REVISION 
information to detect the IP difference, the proper compatible entries 
will indeed have to be used.

> > I'm still a little bit confused about the real need for the
> > "ti,omap4-wdt: entry, but it seems to be the way to do it in PPC.
> >
> > > > > + {},
> > > > > +};
> > > > > +MODULE_DEVICE_TABLE(of, omap_wdt_of_match);
> > > > > +
> > > > > static struct platform_driver omap_wdt_driver = {
> > > > > .probe = omap_wdt_probe,
> > > > > .remove = __devexit_p(omap_wdt_remove),
> > > > > @@ -439,6 +446,7 @@ static struct platform_driver omap_wdt_driver = {
> > > > > .driver = {
> > > > > .owner = THIS_MODULE,
> > > > > .name = "omap_wdt",
> > > > > + .of_match_table = omap_wdt_of_match,
> > > > > },
> > > > > };
> > > >
> > > > I think we need to add some code to the probe function that calls
> > > > of_match_device() and ensures we find a match. For example ...
> > > >
> > > > if (of_have_populated_dt())
> > > > if (!of_match_device(omap_wdt_of_match,&pdev->dev))
> > > > return -EINVAL;
> > > Will add it in v2, thanks for suggestion.
> >
> > No, in fact this is not needed. We need that mainly when several
> > instances can match the same driver and thus we select the proper one
> > using the of_match_device. Otherwise, just check is the device_node is
> > there.
> >
> > In that case, the driver does not even care about any DT node so there
> > is no need to add extra code for that. Keep it simple.
>
> Ok. So are you saying get rid of the match table altogether? In other
> words, drop this patch?

No, the match table is used by the LDM to find the proper driver to be 
bound to a device. So we do need it. But we do not have to use the 
of_match_device if we do not want to get the entry in the device table.

> I agree that it does not really do anything today, but I did not know if
> in the future you were planning to pass things like, register addresses,
> via DT.

Well, yes we will have to, otherwise people will keep complaining that 
our DTS sucks and are not compliant with the DTS standards :-)

Regards,
Benoit
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