6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Russell Senior russell@personaltelco.net
[ Upstream commit bebe35bb738b573c32a5033499cd59f20293f2a3 ]
I still have some Soekris net4826 in a Community Wireless Network I volunteer with. These devices use an AMD SC1100 SoC. I am running OpenWrt on them, which uses a patched kernel, that naturally has evolved over time. I haven't updated the ones in the field in a number of years (circa 2017), but have one in a test bed, where I have intermittently tried out test builds.
A few years ago, I noticed some trouble, particularly when "warm booting", that is, doing a reboot without removing power, and noticed the device was hanging after the kernel message:
[ 0.081615] Working around Cyrix MediaGX virtual DMA bugs.
If I removed power and then restarted, it would boot fine, continuing through the message above, thusly:
[ 0.081615] Working around Cyrix MediaGX virtual DMA bugs. [ 0.090076] Enable Memory-Write-back mode on Cyrix/NSC processor. [ 0.100000] Enable Memory access reorder on Cyrix/NSC processor. [ 0.100070] Last level iTLB entries: 4KB 0, 2MB 0, 4MB 0 [ 0.110058] Last level dTLB entries: 4KB 0, 2MB 0, 4MB 0, 1GB 0 [ 0.120037] CPU: NSC Geode(TM) Integrated Processor by National Semi (family: 0x5, model: 0x9, stepping: 0x1) [...]
In order to continue using modern tools, like ssh, to interact with the software on these old devices, I need modern builds of the OpenWrt firmware on the devices. I confirmed that the warm boot hang was still an issue in modern OpenWrt builds (currently using a patched linux v6.6.65).
Last night, I decided it was time to get to the bottom of the warm boot hang, and began bisecting. From preserved builds, I narrowed down the bisection window from late February to late May 2019. During this period, the OpenWrt builds were using 4.14.x. I was able to build using period-correct Ubuntu 18.04.6. After a number of bisection iterations, I identified a kernel bump from 4.14.112 to 4.14.113 as the commit that introduced the warm boot hang.
https://github.com/openwrt/openwrt/commit/07aaa7e3d62ad32767d7067107db64b6ad...
Looking at the upstream changes in the stable kernel between 4.14.112 and 4.14.113 (tig v4.14.112..v4.14.113), I spotted a likely suspect:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
So, I tried reverting just that kernel change on top of the breaking OpenWrt commit, and my warm boot hang went away.
Presumably, the warm boot hang is due to some register not getting cleared in the same way that a loss of power does. That is approximately as much as I understand about the problem.
More poking/prodding and coaching from Jonas Gorski, it looks like this test patch fixes the problem on my board: Tested against v6.6.67 and v4.14.113.
Fixes: 18fb053f9b82 ("x86/cpu/cyrix: Use correct macros for Cyrix calls on Geode processors") Debugged-by: Jonas Gorski jonas.gorski@gmail.com Signed-off-by: Russell Senior russell@personaltelco.net Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lore.kernel.org/r/CAHP3WfOgs3Ms4Z+L9i0-iBOE21sdMk5erAiJurPjnrL9LSsgR... Cc: Matthew Whitehead tedheadster@gmail.com Cc: Thomas Gleixner tglx@linutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/cpu/cyrix.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/cyrix.c b/arch/x86/kernel/cpu/cyrix.c index 9651275aecd1b..dfec2c61e3547 100644 --- a/arch/x86/kernel/cpu/cyrix.c +++ b/arch/x86/kernel/cpu/cyrix.c @@ -153,8 +153,8 @@ static void geode_configure(void) u8 ccr3; local_irq_save(flags);
- /* Suspend on halt power saving and enable #SUSP pin */ - setCx86(CX86_CCR2, getCx86(CX86_CCR2) | 0x88); + /* Suspend on halt power saving */ + setCx86(CX86_CCR2, getCx86(CX86_CCR2) | 0x08);
ccr3 = getCx86(CX86_CCR3); setCx86(CX86_CCR3, (ccr3 & 0x0f) | 0x10); /* enable MAPEN */