linux-kernel - Re: [PATCH 2/6] mailbox/omap: add support for parsing dt devices

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Message-ID: <20140709082906.GG28884@atomide.com>
Date:	Wed, 9 Jul 2014 01:29:07 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Suman Anna <s-anna@...com>
Cc:	Pavel Machek <pavel@....cz>,
	Jassi Brar <jaswinder.singh@...aro.org>,
	Dave Gerlach <d-gerlach@...com>, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Jassi Brar <jassisinghbrar@...il.com>,
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH 2/6] mailbox/omap: add support for parsing dt devices

* Suman Anna <s-anna@...com> [140708 10:57]:
> Hi Tony, Pavel,
> 
> On 07/04/2014 03:23 AM, Tony Lindgren wrote:
> > * Pavel Machek <pavel@....cz> [140704 01:07]:
> >> Hi!
> >>
> >>>>>>>>> The non-DT support has to be maintained for now to not break
> >>>>>>>>> OMAP3 legacy boot, and the legacy-style code will be cleaned
> >>>>>>>>> up once OMAP3 is also converted to DT-boot only.
> >>>>>>>>
> >>>>>>>>> @@ -587,24 +606,157 @@ static int omap_mbox_unregister(struct omap_mbox_device *mdev)
> >>>>>>>>>  	return 0;
> >>>>>>>>>  }
> >>>>>>>>>  
> >>>>>>>>> +static const struct omap_mbox_device_data omap2_data = {
> >>>>>>>>> +	.num_users	= 4,
> >>>>>>>>> +	.num_fifos	= 6,
> >>>>>>>>> +	.intr_type	= MBOX_INTR_CFG_TYPE1,
> >>>>>>>>> +};
> >>>>>>>>> +
> >>>>>>>>> +static const struct omap_mbox_device_data omap3_data = {
> >>>>>>>>> +	.num_users	= 2,
> >>>>>>>>> +	.num_fifos	= 2,
> >>>>>>>>> +	.intr_type	= MBOX_INTR_CFG_TYPE1,
> >>>>>>>>> +};
> >>>>>>>>> +
> >>>>>>>>> +static const struct omap_mbox_device_data am335x_data = {
> >>>>>>>>> +	.num_users	= 4,
> >>>>>>>>> +	.num_fifos	= 8,
> >>>>>>>>> +	.intr_type	= MBOX_INTR_CFG_TYPE2,
> >>>>>>>>> +};
> >>>>>>>>
> >>
> >>>> Aha, ok, then the intr_type should be derived from
> >>>> compatible-string. Or rather... you should have three
> >>>> compatible-strings for the three possibilities? (And then subtype,
> >>>> currently unused, in case there are more hw differences).
> >>>
> >>> The compatible string can and should be separate for each revision
> >>> unless they are the same exacat hardware revision.
> >>
> >> ACK.
> 
> I checked the revision register from all SoCs. OMAP2 and OMAP3 have
> different revisions compared to OMAP4+. All of OMAP4, OMAP5, DRA7,
> AM335x and AM437x have the same version, but with different num-fifos
> and num-users.  So, I can switch back to using omap4-mailbox for all of
> these SoCs only if we encode the num-fifos and num-users in DT.
> 
> >>
> >>>>> two are HW IP design parameters, so in general putting them in DT isn't
> >>>>> completely a bad idea, but I will wait to see if there are any further
> >>>>> comments on this from Tony or DT maintainers before I make changes.
> >>>>
> >>>> Ok, right... I'd vote for putting them into DT.
> >>>
> >>> I would avoid adding custom DT properties where possible and let the
> >>> driver just initialize the right data based on the compatible flag.
> >>
> >> If these are HW IP design parameters, we can expect to see many
> >> different combinations. Yet we know ahead of time how to handle
> >> different parameters HW people select.
> 
> That's right, the above OMAP4+ SoCs already demonstrate this behavior.
> 
> >>
> >> Thus IMO we should do it in the device tree.
> > 
> > Oh you mean from supporting new hardware with just .dts changes?
> > From that point of view it makes sense to have them as DT properties,
> > so I'm fine with that.
> > 
> > Let's just try to use something that's generic like fifosize. No idea
> > how the property for num_fifos should be handled though as that
> > implies some knowledge in the driver which num_users have fifos?
> 
> The fifos are not per num_users, but rather the total number of fifos
> within the IP block. The num_users will be the number of targets the IP
> block can interrupt. I tried looking for generic properties, but there
> weren't any that seem to fit the description. If you want generic names,
> I can use num-fifos and num-users, otherwise will stick to the
> names defined in the previous series.

OK since we already have some .dts entries with ti,mbox-num-fifos and
ti,mbox-num-users I'd use those for now. Adding parsing for a generic
property can be done later on.

> > So unless that can be described clearly in a DT property as well,
> > the binding might be still unusable for new hardware :)
> > 
> 
> I don't expect the OMAP mailbox IP to change much in the future. There
> is a FIFO depth parameter as well, but that's constant in all the
> current versions, and even if they change it, I can already use the
> generic property for that.

OK
 
> Tony,
> Depending on the agreement here, I may have to respin the OMAP
> mailbox DT/hwmod cleanup series [1]

OK let me know.

Regards,

Tony
 
> [1] http://marc.info/?l=linux-omap&m=140365833121612&w=2
> 
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