Date: Sun, 31 Jul 2016 10:55:47 -0700 From: Thomas Skibo <thomasskibo@yahoo.com> To: freebsd-arm@freebsd.org Subject: Zynq/Zybo USB bug: ubldr "fixes" my device tree Message-ID: <7C4D45AC-3DDB-46FE-85AB-5F692E5C1283@yahoo.com>
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Hello.
I finally tracked down a bug that kept me from being able to use a USB =
drive as root on a Zybo (or Zedboard). Mounting USB drives has worked =
fine before but using one as root would fail.
The first megabyte of memory space on Zynq has several caveats including =
a hole between 256K-512K that is inaccessible by bus masters. My =
solution was to simply ignore the first megabyte by starting memory at =
0x100000 in my DTS file(s). But, I discovered that the first megabyte =
was being allocated and the ehci device hung trying to DMA to the hole. =
It turns out that ubldr, after loading the board.dtb file, proceeded to =
=E2=80=9Cfix up=E2=80=9D the device tree from memory range information =
it got in a sysinfo call to u-boot=E2=80=99s API. The memory range =
started at 0.
The simplest work-around seems to be to add a =E2=80=9Cmemreserve=E2=80=9D=
property to the DTS. Also, It turns out that only the first half =
megabyte needs to be ignored. Patch attached.
=E2=80=94
Thomas Skibo
thomasskibo@yahoo.com
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Index: sys/boot/fdt/dts/arm/zynq-7000.dtsi
===================================================================
--- sys/boot/fdt/dts/arm/zynq-7000.dtsi (revision 303418)
+++ sys/boot/fdt/dts/arm/zynq-7000.dtsi (working copy)
@@ -32,6 +32,10 @@
#size-cells = <1>;
interrupt-parent = <&GIC>;
+ // Reserve first half megabyte because it is not accessible to all
+ // bus masters.
+ memreserve = <0x00000000 0x00080000>;
+
// Zynq PS System registers.
//
ps7sys@f8000000 {
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