linux-kernel - Re: [PATCH RESEND 1/7] arm64: dts: Add APM X-Gene USB DTS node

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Message-ID: <20141110102308.GB21366@e104818-lin.cambridge.arm.com>
Date:	Mon, 10 Nov 2014 10:23:08 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Mark Salter <msalter@...hat.com>
Cc:	Feng Kan <fkan@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"patches@....com" <patches@....com>, Bao Truong <btruong@....com>
Subject: Re: [PATCH RESEND 1/7] arm64: dts: Add APM X-Gene USB DTS node

On Wed, Oct 29, 2014 at 04:23:37PM +0000, Mark Salter wrote:
> On Mon, 2014-10-27 at 12:28 -0700, Feng Kan wrote:
> > This parch adds the device tree nodes for APM X-Gnene USB host controller.
> > Since X-Gene SOC supports maximum 2 USB ports, 2 dts node are added.
> > 
> > Signed-off-by: Bao Truong <btruong@....com>
> > Signed-off-by: Feng Kan <fkan@....com>
> > ---
> >  arch/arm64/boot/dts/apm-storm.dtsi | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/apm-storm.dtsi b/arch/arm64/boot/dts/apm-storm.dtsi
> > index 3eef74b..a80f2fa 100644
> > --- a/arch/arm64/boot/dts/apm-storm.dtsi
> > +++ b/arch/arm64/boot/dts/apm-storm.dtsi
> > @@ -587,6 +587,20 @@
> >  			phy-names = "sata-phy";
> >  		};
> >  
> > +		usb0: dwusb@...00000 {
> > +			status = "disabled";
> > +			compatible = "xhci-platform";
> > +			reg =  <0x0 0x19000000 0x0 0x100000>;
> > +			interrupts = <0x0 0x89 0x4>;
> > +		};
> > +
> > +		usb1: dwusb@...00000 {
> > +			status = "disabled";
> > +			compatible = "xhci-platform";
> > +			reg =  <0x0 0x19800000 0x0 0x100000>;
> > +			interrupts = <0x0 0x8a 0x4>;
> > +		};
> > +
> 
> Should these have "dma-coherent" properties?

Just a note here: if the device is coherent but the DT does not specify
it as such, it's not just a matter of performance but potentially data
corruption. The current DMA ops for non-coherent devices perform a
D-cache invalidate on the unmap path with the FROM_DEVICE direction. If
the device is coherent and the DMA transfer (FROM_DEVICE) allocated data
in the system cache (L3), the CPU cache invalidation after the transfer
would corrupt such data.

We had a similar discussion internally around coherency properties for
ACPI. If we don't have guarantees that the DT (or ACPI) tables always
pass the correct information, we should change the kernel DMA ops to
perform the safe clean+invalidate on the unmap path (some CPU
implementations do this by default).

-- 
Catalin
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