linux-kernel - Re: [PATCH v7 08/12] arm: dts: s5pv210: Add node for SGX 540

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Date:   Sun, 26 Apr 2020 07:57:12 -0700
From:   Jonathan Bakker <xc-racer2@...e.ca>
To:     Paul Cercueil <paul@...pouillou.net>,
        "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     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>,
        Tony Lindgren <tony@...mide.com>,
        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>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Philipp Rossak <embed3d@...il.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        openpvrsgx-devgroup@...ux.org, letux-kernel@...nphoenux.org,
        kernel@...a-handheld.com, linux-mips@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH v7 08/12] arm: dts: s5pv210: Add node for SGX 540

Hi Paul,

On 2020-04-26 5:56 a.m., Paul Cercueil wrote:
> 
> 
> Le ven. 24 avril 2020 à 22:34, H. Nikolaus Schaller <hns@...delico.com> a écrit :
>> From: Jonathan Bakker <xc-racer2@...e.ca>
>>
>> All s5pv210 devices have a PowerVR SGX 540 (revision 120) attached.
>>
>> There is no external regulator for it so it can be enabled by default.
>>
>> Signed-off-by: Jonathan Bakker <xc-racer2@...e.ca>
>> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
>> ---
>>  arch/arm/boot/dts/s5pv210.dtsi | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/s5pv210.dtsi b/arch/arm/boot/dts/s5pv210.dtsi
>> index 2ad642f51fd9..abbdda205c1b 100644
>> --- a/arch/arm/boot/dts/s5pv210.dtsi
>> +++ b/arch/arm/boot/dts/s5pv210.dtsi
>> @@ -512,6 +512,19 @@ vic3: interrupt-controller@...00000 {
>>              #interrupt-cells = <1>;
>>          };
>>
>> +        gpu: gpu@...00000 {
>> +            compatible = "samsung,s5pv210-sgx540-120";
>> +            reg = <0xf3000000 0x10000>;
>> +            interrupt-parent = <&vic2>;
>> +            interrupts = <10>;
>> +            clock-names = "core";
>> +            clocks = <&clocks CLK_G3D>;
>> +
>> +            assigned-clocks = <&clocks MOUT_G3D>, <&clocks DOUT_G3D>;
>> +            assigned-clock-rates = <0>, <66700000>;
>> +            assigned-clock-parents = <&clocks MOUT_MPLL>;
> 
> What are these clocks for, and why are they reparented / reclocked?
> 
> Shouldn't they be passed to 'clocks' as well?
> 
> -Paul
> 

The G3D clock system can have multiple parents, and for stable operation
it's recommended to use the MPLL clock as the parent (which in turn
is actually a mux as well).  MOUT_G3D is simply the mux for CLK_G3D
(SGX core clock), DOUT_G3D is the divider.  DOUT_G3D could equally be CLK_G3D
(and probably should be, for readability) as CLK_G3D is simply the gate and
DOUT_G3D is the divider for it.

The SGX clock layout on S5PV210 looks something like this:

        MOUT_MPLL -----------> MOUT_G3D ---> DOUT_G3D  ---> CLK_G3D
(selectable parent clock)      (mux)    ---> (divider) ---> (gate)

This is fairly common for older Samsung SoCs, eg having a look at
arch/arm/boot/dts/exynos4210-universal_c210.dts you can see that
the FIMC clocks are parented to MPLL and have a rate set.

>> +        };
>> +
>>          fimd: fimd@...00000 {
>>              compatible = "samsung,s5pv210-fimd";
>>              interrupt-parent = <&vic2>;
>> -- 
>> 2.25.1
>>
> 
> 

Thanks,
Jonathan