Re: [PATCH 0/8] Basic ARM device tree support
From: Jason Liu
Date: Fri Jan 28 2011 - 01:37:23 EST
2011/1/27 Rob Herring <robherring2@xxxxxxxxx>:
> On 01/26/2011 02:04 PM, John Linn wrote:
>>> -----Original Message-----
>>> From: Grant Likely [mailto:glikely@xxxxxxxxxxxx] On Behalf Of Grant
>>> Sent: Tuesday, January 18, 2011 1:29 PM
>>> To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>>> Cc: Nicolas Pitre; Russell King; Catalin Marinas;
>>> devicetree-discuss@xxxxxxxxxxxxxxxx; linux-
>>> kernel@xxxxxxxxxxxxxxx; Olof Johansson; Jeremy Kerr; John Linn; Lennert
>>> Subject: [PATCH 0/8] Basic ARM device tree support
>>> It's been a while since these patches have been circulated for review.
>>> Much has changed since the last posting and there are no longer any
>>> ugly hacks or workarounds to it working. From my viewpoint, these
>>> patches are complete and ready to be used.
>>> This patch series allows CONFIG_OF to be enabled on ARM and allows the
>>> kernel to accept a dtb pointer from boot firmware instead of atags.
>>> If a dtb is passed, then the kernel will use the root 'compatible'
>>> property to find a matching machine_desc, and it will use it to obtain
>>> the memory layout, initrd location and kernel parameters string.
>>> Only limited device tree support is enabled here. It does not perform
>>> any kind of device registration from device tree data. That support
>>> will be enabled in a later patch set. Right now those patches depend
>>> on the common struct clk patches that Jeremy is working on, so I'm not
>>> going to post them yet. Rather, this series is a stable base that
>>> other engineers can use to start working on device tree support for
>>> their platforms.
>>> Tested on Versatile (qemu) and nVidia Tegra Harmony. Kernel compiles
>>> an boot with CONFIG_OF both on and off, both with and without passing
>>> a device tree blob.
>> Tested on Xilinx platform. Did see an issue with loading the device
>> tree blob into higher memory. At address 0 there was no issue.
> I have a fix for this. The issue is the early mmu page table needs to map
> the dtb. I later realized this is also may be problem for ATAGs as well, so
> I planned to re-work to make it unconditional and work for ATAGs. Or perhaps
> ATAGs only get accessed with the MMU on later than the dtb and everything is
> This applies to the DT patch set prior to the one Grant sent out
> this week, so it may need updates.
> From: Rob Herring <rob.herring@xxxxxxxxxxx>
> Date: Tue, 5 Oct 2010 10:32:51 -0500
> Subject: [PATCH] arm/dt: map devtree blob in initial page table
> If the DTB is not in 1st 1MB of RAM, it will not be mapped before
> memblock is setup, so map it early. We assume the dtb is less than
> 1MB and map 2MB so it can be at any alignment.
> Some assembly optimizations from Nicolas Pitre.
> Signed-off-by: Rob Herring <rob.herring@xxxxxxxxxxx>
> arch/arm/kernel/head.S | 13 +++++++++++++
> 1 files changed, 13 insertions(+), 0 deletions(-)
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index 0480f25..1fcb962 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -228,6 +228,19 @@ __create_page_tables:
> str r6, [r0]
> +#ifdef CONFIG_OF_FLATTREE
> + /* Make sure DT blob is mapped */
> + adr r0, __devtree_pointer
> + ldr r0, [r0]
> + mov r0, r0, lsr #20
> + mov r0, r0, lsl #20
> + add r3, r0, #PAGE_OFFSET
> + add r3, r4, r3, lsr #18
> + orr r6, r7, r0
> + str r6, [r3]
> + add r6, r6, #0x100000
> + str r6, [r3, #4]
> #ifdef CONFIG_DEBUG_LL
> #ifndef CONFIG_DEBUG_ICEDCC
Build broken after apply your patch,
arch/arm/kernel/head.S:223: Error: undefined symbol __devtree_pointer
used as an immediate value
make: *** [arch/arm/kernel/head.o] Error 1
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