linux-kernel - 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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Message-ID: <20200422065859.quy6ane5v7vsy5tf@gilmour.lan>
Date:   Wed, 22 Apr 2020 08:58:59 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Tony Lindgren <tony@...mide.com>,
        Philipp Rossak <embed3d@...il.com>,
        Jonathan Bakker <xc-racer2@...e.ca>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Benoît Cousson <bcousson@...libre.com>,
        Paul Cercueil <paul@...pouillou.net>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paulburton@...nel.org>,
        James Hogan <jhogan@...nel.org>, Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "open list:DRM PANEL DRIVERS" <dri-devel@...ts.freedesktop.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        OpenPVRSGX Linux Driver Group <openpvrsgx-devgroup@...ux.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, kernel@...a-handheld.com,
        linux-mips@...r.kernel.org,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc@...r.kernel.org
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)

On Tue, Apr 21, 2020 at 07:29:32PM +0200, H. Nikolaus Schaller wrote:
> 
> > Am 21.04.2020 um 16:15 schrieb Tony Lindgren <tony@...mide.com>:
> > 
> > * Maxime Ripard <maxime@...no.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.
> >>> 
> >>> It is basically some bit that verify that the clocks should be enabled or
> >>> disabled.
> >> 
> >> 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.
> > 
> > Note that on omaps there are actually SoC module specific registers.
> 
> 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.
> 
> This indeed seems to be unique with omap.
> 
> > And there can be multiple devices within a single target module on
> > omaps. So the extra dts node and device is justified there.
> > 
> > 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.
> 
> That is why we need to evaluate what the better strategy is.
> 
> So we have
> a) omap which has a custom wrapper around the sgx
> b) others without, i.e. an empty (or pass-through) wrapper
> 
> Which one do we make the "standard" and which one the "exception"?
> What are good reasons for either one?
> 
> 
> 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).
> 
> This will likely avoid problems if we find more SoC with yet another
> scheme how the SGX clocks are wrapped.
> 
> 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.

I disagree. Every other GPU binding and driver is handling that just fine, and
the SGX is not special in any case here.

Maxime

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