From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jisheng Zhang Subject: Re: [PATCH] ARM: dts: chromecast: override bad bootloader memory info Date: Tue, 15 May 2018 10:29:39 +0800 Message-ID: <20180515102939.3ab8797c@xhacker.debian> References: <20180514215645.17592-2-tommyhebb@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180514215645.17592-2-tommyhebb@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Thomas Hebb Cc: linux-kernel@vger.kernel.org, Sebastian Hesselbarth , Rob Herring , Mark Rutland , "moderated list:ARM/Synaptics Berlin SoC support" , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" List-Id: devicetree@vger.kernel.org Hi, On Mon, 14 May 2018 17:56:45 -0400 Thomas Hebb wrote: > On the Chromecast, the bootloader provides us with an ATAG_MEM of > start=0x01000000 and size=0x3eff8000. This is clearly incorrect, as the > range given encompasses nearly a GiB but the Chromecast only has 512MiB > of RAM! Additionally, this causes the kernel to be decompressed at > 0x00008000, below the claimed beginning of RAM, and so the boot fails. > > Since the existing ATAG parsing code runs before the kernel is even > decompressed and irrevocably patches the device tree, don't even try This means you enabled ARM_ATAG_DTB_COMPAT. could we disable it instead? The ATAG is useless when we provide dtb. And IIRC, the ATAG is provided due to legacy history code. Thanks > to bypass it. Instead, use the "linux,usable-memory" property instead > of the "reg" property to define the real range. The ATAG code only > overwrites reg, but linux,usable-memory is checked first in the OF > driver, so the fact that reg gets changed makes no difference. > > Signed-off-by: Thomas Hebb > --- > arch/arm/boot/dts/berlin2cd-google-chromecast.dts | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/boot/dts/berlin2cd-google-chromecast.dts b/arch/arm/boot/dts/berlin2cd-google-chromecast.dts > index 20f31cdeaf38..54221f55bfa2 100644 > --- a/arch/arm/boot/dts/berlin2cd-google-chromecast.dts > +++ b/arch/arm/boot/dts/berlin2cd-google-chromecast.dts > @@ -52,7 +52,17 @@ > > memory@0 { > device_type = "memory"; > - reg = <0x00000000 0x20000000>; /* 512 MB */ > + > + /* > + * We're using "linux,usable-memory" instead of "reg" here > + * because the (signed and encrypted) bootloader that shipped > + * with this device provides an incorrect memory range in > + * ATAG_MEM. Linux helpfully overrides the "reg" property with > + * data from the ATAG, so we can't specify the proper range > + * normally. Fortunately, this alternate property is checked > + * first by the OF driver, so we can (ab)use it instead. > + */ > + linux,usable-memory = <0x00000000 0x20000000>; /* 512 MB */ > }; > > leds {