[U-Boot] CONFIG_REVISION (was i.MX6: mx6qsabrelite: allow use with Freescale 2.6.38 kernels)

Stefano Babic sbabic at denx.de
Wed Mar 7 09:43:47 CET 2012

On 04/03/2012 20:45, Eric Nelson wrote:

> The linkage is really indirect. The ATAG item is still supported in the
> main-line kernel for ARM:
>     http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=arch/arm/kernel/setup.c;h=a255c39612ca3cfa10bddb7c7728216efeeb04d5;hb=HEAD#l704
> The breakage I noticed was in the VPU driver, which refused to load
> with a zero-value in system_rev. The net result was no video playback
> in the Freescale Android ICS release.

However, I have not found a statement in FSL's kernel where system_rev
in VPU driver is checked, directly or indirectly - neither in VPU driver
nor in the board initialization code, nor in another MXC driver.
It seems to me a side-effect in FSL's kernel, and for some not yet known
reasons the problem disappears with this tag - or can reappear later,
because we do not know the cause.

And if I am not wrong, there are two macros in FSL's kernel checking the
system_rev (arch/arm/plat-mxc/include/mach/mxc.h):

#define imx_cpu_ver()		(system_rev & 0xFF)
#define board_is_rev(rev)	(((system_rev & 0x0F00) == rev) ? 1 : 0)

But you defines board_rev as:
> +u32 get_board_rev(void)
> +{
> +	return 0x63000 ;

Both macro still return 0x00...there is no change if the ATAG is not
set. Sure that the problem you report is really bound to system_rev ? I
am quite OT here, we are investigating an issue in FSL kernel on the
U-boot ML.

Anyway, the ATAG is supported and as I already said quite common for
U-Boot boards. The commit message " Freescale 2.6.38 (Non-DT) kernels
require the revision atag to enable the VPU." should be extended
explaining the real cause (if known) or changed dropping VPU because
there is no clear relationship between the ATAG and the issue.

Best regards,
Stefano Babic

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