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

From: Suman Anna
Date: Tue Jul 08 2014 - 13:56:03 EST

Hi Tony, Pavel,

On 07/04/2014 03:23 AM, Tony Lindgren wrote:
> * Pavel Machek <pavel@xxxxxx> [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.

> 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.

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



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