On 22/03/17 16:01, Leo Yan wrote:

On Wed, Mar 22, 2017 at 02:07:47PM +0000, Sudeep Holla wrote:

[...]

quoted

We can always do that unconditionally. If implementations don't honor
those bits, it's different. If they hang on accessing something which is
on debug power domain and not on core power domain, then you have much
bigger issue to solve. How can you even trust and make any other
register accesses that are in debug power domain then ?

So we can add below code before really access another other registers
are possible in CPU power domain:

        /*
         * Force to power on CPU power domain and assert
         * DBGPWRUPREQ signal
         */
        val = readl(drvdata->base + EDPRCR);
        val |= BIT(3);
        writel(val, drvdata->base + EDPRCR);

Yes worth trying it out.

[...]

I tried to digest these info and below are my understanding from your
suggestion:

### For boot time: add two command line flags

I am not really sure about boot flags as there are dependency on power
domains and expecting them to be powered on quite earlier is too much to
ask. I am not sure if we need special case for boot time. But that's
just my opinion. If someone has found it *really* useful and no other
alternative exists, then go for it.

[...]

### For runtime: use one sysfs node

- Create sysfs node:
  /sys/kernel/debug/coresight_cpu_debug/enable_debug

  echo 1 > /sys/kernel/debug/coresight_cpu_debug/enable_debug: same
  functionality with boot time's 'coresight.cpu_debug';

My argument was this to be default without any need for flags.
We can skip it as and when we find broken implementation if required.

  echo 2 > /sys/kernel/debug/coresight_cpu_debug/enable_debug: same
  functionality with boot time's 'coresight.cpu_debug_pwrup';

  echo 0 > /sys/kernel/debug/coresight_cpu_debug/enable_debug: disable
  debug functionality.

So it can be simple boolean to force setup the power domain requirements
for it to work whenever you need to activate it. I may be missing some
use-case, but IIUC simple boolean flag should be fine as suggested
initially.

-- 
Regards,
Sudeep