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Subject: Re: [PATCH v6 00/12] ARM/MIPS: DTS: add child nodes describing the PVRSGX GPU present in some OMAP SoC and JZ4780 (and many more)
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From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <20200422065859.quy6ane5v7vsy5tf@gilmour.lan>
Date:   Wed, 22 Apr 2020 09:10:57 +0200
Cc:     Tony Lindgren <tony@atomide.com>,
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        Jonathan Bakker <xc-racer2@live.ca>,
        David Airlie <airlied@linux.ie>,
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        James Hogan <jhogan@kernel.org>, Kukjin Kim <kgene@kernel.org>,
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To:     Maxime Ripard <maxime@cerno.tech>
Sender: linux-kernel-owner@vger.kernel.org
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Hi Maxime,

> Am 22.04.2020 um 08:58 schrieb Maxime Ripard <maxime@cerno.tech>:
>=20
> On Tue, Apr 21, 2020 at 07:29:32PM +0200, H. Nikolaus Schaller wrote:
>>=20
>>> Am 21.04.2020 um 16:15 schrieb Tony Lindgren <tony@atomide.com>:
>>>=20
>>> * Maxime Ripard <maxime@cerno.tech> [200421 11:22]:
>>>> On Tue, Apr 21, 2020 at 11:57:33AM +0200, Philipp Rossak wrote:
>>>>> I had a look on genpd and I'm not really sure if that fits.
>>>>>=20
>>>>> It is basically some bit that verify that the clocks should be =
enabled or
>>>>> disabled.
>>>>=20
>>>> No, it can do much more than that. It's a framework to control the =
SoCs power
>>>> domains, so clocks might be a part of it, but most of the time it's =
going to be
>>>> about powering up a particular device.
>>>=20
>>> Note that on omaps there are actually SoC module specific registers.
>>=20
>> Ah, I see. This is of course a difference that the TI glue logic has
>> its own registers in the same address range as the sgx and this can't
>> be easily handled by a common sgx driver.
>>=20
>> This indeed seems to be unique with omap.
>>=20
>>> And there can be multiple devices within a single target module on
>>> omaps. So the extra dts node and device is justified there.
>>>=20
>>> For other SoCs, the SGX clocks are probably best handled directly
>>> in pvr-drv.c PM runtime functions unless a custom hardware wrapper
>>> with SoC specific registers exists.
>>=20
>> That is why we need to evaluate what the better strategy is.
>>=20
>> So we have
>> a) omap which has a custom wrapper around the sgx
>> b) others without, i.e. an empty (or pass-through) wrapper
>>=20
>> Which one do we make the "standard" and which one the "exception"?
>> What are good reasons for either one?
>>=20
>>=20
>> I am currently in strong favour of a) being standard because it
>> makes the pvr-drv.c simpler and really generic (independent of
>> wrapping into any SoC).
>>=20
>> This will likely avoid problems if we find more SoC with yet another
>> scheme how the SGX clocks are wrapped.
>>=20
>> It also allows to handle different number of clocks (A31 seems to
>> need 4, Samsung, A83 and JZ4780 one) without changing the sgx =
bindings
>> or making big lists of conditionals. This variance would be handled
>> outside the sgx core bindings and driver.
>=20
> I disagree. Every other GPU binding and driver is handling that just =
fine, and
> the SGX is not special in any case here.

Can you please better explain this? With example or a description
or a proposal?

I simply do not have your experience with "every other GPU" as you have.
And I admit that I can't read from your statement what we should do
to bring this topic forward.

So please make a proposal how it should be in your view.

BR and thanks,
Nikolaus