Re: [PATCH v7 0/4] arm: Fix DEBUG_LL for multi-platform kernels (without PL01X)

Daniel Thompson
2014-07-14T09:06:18Z

On 12/07/14 12:10, Russell King - ARM Linux wrote:
> On Sat, Jul 12, 2014 at 11:16:02AM +0100, Russell King - ARM Linux wrote:
>> On Mon, Jun 30, 2014 at 12:30:51PM +0100, Daniel Thompson wrote:
>>> This patchset removes some single-platform compatibility tricks related
>>> to DEBUG_LL and, as a result, allows multi_v7_defconfig derived builds
>>> to enable DEBUG_LL. Currently the user selected kbuild setting is
>>> ignored and the PL01X's DEBUG_LL stub is silently selected instead. This
>>> is a pain if your hardware doesn't have this cell, not least because it
>>> takes a little time to figure out that kbuild built the wrong code.
>>
>> I don't think this is quite right, because I'm now seeing randconfig
>> finding build errors with this. We can end up with this configuration:
>>
>> CONFIG_DEBUG_LL=y
>> CONFIG_DEBUG_LL_UART_NONE=y
>> # CONFIG_DEBUG_ICEDCC is not set
>> # CONFIG_DEBUG_SEMIHOSTING is not set
>> # CONFIG_DEBUG_LL_UART_8250 is not set
>> # CONFIG_DEBUG_LL_UART_PL01X is not set
>> CONFIG_DEBUG_LL_INCLUDE="mach/debug-macro.S"
>> # CONFIG_DEBUG_UART_8250 is not set
>>
>> which results in:
>>
>> arch/arm/kernel/debug.S:24:33: fatal error: mach/debug-macro.S: No such file or directory
>> make[2]: *** [arch/arm/kernel/debug.o] Error 1
>> arch/arm/kernel/head.S:27:33: fatal error: mach/debug-macro.S: No such file or directory
>> make[2]: *** [arch/arm/kernel/head.o] Error 1
>> Full config file:
>> http://www.arm.linux.org.uk/developer/build/file.php?lid=11023

Thanks. I will look at this.

Problem is that by making the build system honour the user choice we end
up breaking the build when the user makes a bad choice (albeit a bad
choice that they should not have been given in the first place).

I guess the best fix is to get rid of CONFIG_DEBUG_LL_UART_NONE altogether.

> Note that this also breaks building versatile as an oldconfig. I'll drop
> the patch series from my tree for the time being.

There is a difficult problem with oldconfig.

Today DEBUG_LL only works on versatile defconfigs (and oldconfig
upgrades from there) because although CONFIG_DEBUG_LL_UART_NONE is
selected the build system does not honour this and behaves as though the
use selected CONFIG_DEBUG_LL_UART_PL01X instead.

Unfortunately if we fix this and remove CONFIG_DEBUG_LL_UART_NONE as
proposed above then the oldconfig will silently select
CONFIG_DEBUG_SEMIHOSTING.

In other words I will be able to offer a patch so that oldconfig
*compiles* but I don't know how to get it to preserve behaviour (or
whether this matters).

Hints about what to do would be very welcome.

Daniel.