Greetings,

I'm trying to enable the Coresight ETMv4 trace from kernel mode. I saw there is no documentation on how to do this, except using the sysfs user mode interface and perf. 

To overcome this i looked a little bit in the coresight.h header file, and came to these APIs:
extern int coresight_enable(struct coresight_device *csdev);                                      
extern void coresight_disable(struct coresight_device *csdev);  

And the sysfs implementation uses these APIs when enabing/disabling the trace code, so i thought this could suit my needs. The next problem was actually getting the coresight devices data structures, which aren't exported and are actually provided internally to perf and sysfs. So i exported the coresight bus type:

struct bus_type coresight_bustype = {                                                              
        .name   = "coresight",                                                  
};                                                                              
EXPORT_SYMBOL(coresight_bustype);     

And enumerated the bus and just looked for the type CORESIGHT_DEV_TYPE_SOURCE, since the only source on my board is ETMv4, there isn't any conflicts so i should get only ETMv4s.

This worked, and indeed i collected a coresight device for every CPU, and enabled the trace successfully while being in non-atomic context. 

The problem is, i must enable the trace in atomic context synchronously on the current thread's CPU(i can't issue a work-queue to enable the trace for me). So.. i got many BUG() errors  because of non-atomic API usage, for example, the allocation of the TMC-ETR buffer:
dma_alloc_coherent(drvdata->dev, etr_buf->size,                          
                                  &flat_buf->daddr, GFP_KERNEL);

So my questions are:

1) Is there a more documented way of enabling coresight from kernel mode? i believe i achieved this using cheats.
2) I see there is no exported kernel API to config the coresight trace attributes(for example, filter EL0). I can only do so from sysfs.. am i missing something?
3) Are there any plans to make the Coresight infrastructure atomic-context friendly?
If there are, is the development in progress? if not.. how would you suggest tackling the issues i've described in this message?

Thank you!