linux-kernel - Re: [PATCH] DTS: bcm2711: Move emmc2 into its own bus

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Date:   Tue, 03 Mar 2020 19:32:49 +0100
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, florian.fainelli@...adcom.com,
        phil@...pberrypi.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] DTS: bcm2711: Move emmc2 into its own bus

Hi Florian,

On Tue, 2020-03-03 at 10:21 -0800, Florian Fainelli wrote:
> On 3/3/20 4:08 AM, Nicolas Saenz Julienne wrote:
> > Depending on bcm2711's revision its emmc2 controller might have
> > different DMA constraints. Raspberry Pi 4's firmware will take care of
> > updating those, but only if a certain alias is found in the device tree.
> > So, move emmc2 into its own bus, so as not to pollute other devices with
> > dma-ranges changes and create the emmc2bus alias.
> > 
> > Based in Phil ELwell's downstream implementation.
> > 
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> 
> Nit: the subject should be ARM: dts: bcm2711. Some more comments below.

Of course, should have known better.

> > ---
> >  arch/arm/boot/dts/bcm2711-rpi-4-b.dts |  1 +
> >  arch/arm/boot/dts/bcm2711.dtsi        | 19 ++++++++++++++-----
> >  2 files changed, 15 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> > b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> > index 1d4b589fe233..e26ea9006378 100644
> > --- a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> > +++ b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> > @@ -20,6 +20,7 @@ memory@0 {
> >  	};
> >  
> >  	aliases {
> > +		emmc2bus = &emmc2bus;
> >  		ethernet0 = &genet;
> >  		pcie0 = &pcie0;
> >  	};
> > diff --git a/arch/arm/boot/dts/bcm2711.dtsi b/arch/arm/boot/dts/bcm2711.dtsi
> > index d1e684d0acfd..61ea8b44c51e 100644
> > --- a/arch/arm/boot/dts/bcm2711.dtsi
> > +++ b/arch/arm/boot/dts/bcm2711.dtsi
> > @@ -241,17 +241,26 @@ pwm1: pwm@...0c800 {
> >  			status = "disabled";
> >  		};
> >  
> > +		hvs@...00000 {
> > +			interrupts = <GIC_SPI 97 IRQ_TYPE_LEVEL_HIGH>;
> > +		};
> > +	};
> > +
> > +	emmc2bus: emmc2bus {
> > +		compatible = "simple-bus";
> > +		#address-cells = <2>;
> > +		#size-cells = <1>;
> > +
> > +		ranges = <0x0 0x7e000000  0x0 0xfe000000  0x01800000>;
> > +		dma-ranges = <0x0 0xc0000000  0x0 0x00000000  0x40000000>;
> 
> This deserves a comment for two reasons:
> 
> - explaining which of these properties is getting patched by the
> firmware (and it would be really nice if we had a concept of annotation
> attributes for Device Tree such that you could express something like:
> 
> 	dma-ranges = <> __patchable;

Something like this would've been useful to me some time ago while debugging
CMA issues on a random arm64 Board. I was left wondering if the memory nodes on
that specific board were set in stone or just a placeholder.

> - explaining why this is not collapsed in the soc bus node, because the
> dma-ranges constraint can be different based on the Pi4 revision

Noted

> With that fixed, this looks good to me!

Thanks!

> 
> > +
> >  		emmc2: emmc2@...40000 {
> >  			compatible = "brcm,bcm2711-emmc2";
> > -			reg = <0x7e340000 0x100>;
> > +			reg = <0x0 0x7e340000 0x100>;
> >  			interrupts = <GIC_SPI 126 IRQ_TYPE_LEVEL_HIGH>;
> >  			clocks = <&clocks BCM2711_CLOCK_EMMC2>;
> >  			status = "disabled";
> >  		};
> > -
> > -		hvs@...00000 {
> > -			interrupts = <GIC_SPI 97 IRQ_TYPE_LEVEL_HIGH>;
> > -		};
> >  	};
> >  
> >  	arm-pmu {
> > 
> 
> 


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