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 <tommyhebb@xxxxxxxxx>
> ---
> 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 {
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