Any SYSRQ key to force mode switch to console mode when using KMS?

Jason Wessel jason.wessel at
Wed Oct 6 11:44:48 PDT 2010

On 09/24/2010 10:07 AM, Randy Dunlap wrote:
> On Thu, 23 Sep 2010 18:31:32 +0200 Uwe Bonnes wrote:
> [just adding cc's]
>>>>>>> "Randy" == Randy Dunlap <rdunlap at> writes:
>>     Randy> Is CONFIG_DRM_KMS_HELPER enabled in your kernel .config file?  If
>>     Randy> not, we need to find out how to enable it (there is no kconfig
>>     Randy> prompt for it).
>> Yes, it is enabled
>>     Randy> Can you check if Alt-Sysrq-H (help) lists V for "force-fb(V)"?
>> Yes, it is listed.
>> And yes, my last experiments where with ALT-CTL-sysreq, so doomed for non
>> function due to operator error.
>> However:
>> When running X, X.Org X Server 1.9.0 on Thinkpad R50 RV250, Alt-Sysrq-v
>> switches to an all-black display. By console switching with ALT-CLT-F1 I
>> get back to the booting console and ALT-CLT-F7 brings me back to X.  Running
>> on the console and calling Alt-Sysrq-v prints
>>  SysRq : Restore framebuffer console
>> Is there some omission by the distribution or my setup that Alt-Sysrq-v when
>> running X results in an all-black screen?
>> And when I hit the hibernate problem, the screen stays black even with a
>> console switch after Alt-Sysrq-v
I am not exactly sure what you are looking for but alt-sysrq-v might not
tell you a whole lot because an escape back to the text console that was
not actively receiving printk's or crash data is going to in general
provide you with a black screen.

If you were interested in something a bit more invasive such as a
collecting a process listing or examining the dmesg output you might
consider jumping into kdb.  

echo kbd > /sys/module/kgdboc/parameters/kgdboc

Then you would do the "alt-sysrq v" followed by "alt-sysrq g".  From
there you could then run dmesg, and your screen would no longer be blank
in theory.  :-)

We do have some patches for the RV250 for atomic kernel mode setting
plus kdb support but they are not merged to the mainline kernels as of yet.


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