Hi to all.
In my last message I wrote:
"Now I'm starting again from start but with different knowledge level."
and now I have some preliminary results and another set of issues/questions.
After making run/log work on single core I had two possible directions to take: device drivers or enable smp. I started with smp as with the device drivers I need an advice about build system (later in this email).
For SMP on RPI I implemented new timer driver as the current one was not capable to support multiple independent timers for cores and new PIC driver - for timer and inter processor interrputs.
Current code is in (rewritten) same branch as previously at [1] in case you wanted to look. run/smp test is almost working on all cores with the exception for thread cleanup (which will be another question later in email).
1. Register sets.
On multicore Raspbery Pi there are sets of registers in which each register has the same structure and each is "assigned" to different core. Currently I replicated definitions of registers for each core [2] but it's obviously not a good solution. Additionally it forces to write ugly code when cpu_id is in the variable as in [3].
Is there some support in Genode for such structures? If not, do you see how that could be implemented? Some wrapper for Register? I fail to see how dynamic value of 'cpu_id' could be nicely mixed with register offsets passed as template arguments.
I think ideally it would be to define something like this:
struct CoreTIrqCtl : RegisterSet<0x40, 32, COUNT, OFFSET>
and use it like this:
write<CoreTIrqCtl>(CPU_ID, 0);
Any thoughts?
2. Interrupts handling
I have doubts about interrupts processing. I have limited knowledge in this area so I may be totally wrong but based on what I read for RPI I think that:
a. On one IRQ there can be more than one interrupt flag marking an exception. During this one entry to 'Thread::exception(Cpu&)' and later to 'Cpu_job::_interrupt(unsigned const)' all pending interrupts should be handled in some loop. Without that some interrupts may stay unhandled. And I don't see such loop in this code. One exception is taken from Pic driver, handled and that's all.
b. I don't know where clearing an interrupt should be handled. I would have thought that 'Pic::finish_request()' would be good for this, but there are many empty implementations. Should code in 'Pic::take_exception(...) also clear the exception condition? My doubts come from feeling that if I do this too early "something" can happen before handling of interrupt is finished.
If 'finish_request()' is a proper place to clear interrupt as handled than it would be useful to pass to it interrupt number earlier returned from 'take_request'. Otherwise there would have to be separate storage for each core in Pic to store information about currently handled exception on a given core. Am I right? Does it work properly in [4]?
3. run/smp test hangs during threads destruction
Like I wrote earlier run/smp test is almost working on multiple cores. It hangs somewhere in [5] during destructing thread running non-zero core (destroying first one does not cause problems).
I don't have any concrete questions here. The only ones are:
a. Does this test properly work on arndale?
b. Do you have any thoughts what can go wrong? Maybe I haven't implemented something important for smp yet? Only timer and IPI?
4. Drivers reused for different configurations
Currently to support RPI3 I created configurations named 'rpi3bplus'. How should I proceed to reuse a driver written for rpi? For example framebuffer driver has 'REQUIRES = rpi' in target.mk [6] and that causes that it does not compile for my 'rpi3bplus'. It would be nice to have: 'REQUIRES = rpi|rpi3bplus' but I don't think it is possible. Can you suggest something?
Tomasz Gajewski
[1] https://github.com/tomga/genode/tree/rpi3bplus [2] https://github.com/tomga/genode/blob/rpi3bplus/repos/base-hw/src/core/spec/r... [3] https://github.com/tomga/genode/blob/rpi3bplus/repos/base-hw/src/core/spec/r... [4] https://github.com/tomga/genode/blob/rpi3bplus/repos/base-hw/src/lib/hw/spec... [5] https://github.com/tomga/genode/blob/rpi3bplus/repos/base/src/test/smp/main.... [6] https://github.com/tomga/genode/blob/rpi3bplus/repos/os/src/drivers/framebuf...