Re: [PATCH v23 08/22] cxl/hdm: Add support for getting region from committed decoder

[Dan Williams <dan.j.williams@intel.com>]

PJ Waskiewicz wrote:
[..]
> > Yes, I think you are right. This works in my tests and it is safe 
> > because I check the region does exist before using it. But the error 
> > inside sfc should then not be fatal for cxl sfc initialization and 
> > fallback to the other cxl initialization possibility.
> > 
> 
> So I'm running into this situation I think.
> 
> When you're testing, are you surviving a reload of the driver?  Right
> now, I can load and successfully create the region0 device.  However,
> following the same teardown path in SFC, I cannot reload my driver
> afterwards and map the region.  I get:
> 
> cxl_port endpoint5: failed to attach decoder5 to region0: -6  (ENXIO)
> <driver> 0000:c1:00.0: CXL found committed decoder without a region
> <driver> 0000:c1:00.0: CXL init failed
> 
> I'd be surprised if SFC in its current patch state would survive this
> same insmod/rmmod/insmod test.

So over here [1] I reviewed Smita's patch to stop resetting decoders by
default if they were part of region auto-assembly. While that stops
resetting the decoders it does not allow the device to get a hint of
where it should place its HPAs if the decoders get reset while the
driver is detached.

I am going to draft some patches to allow an accelerator to mark an
address range as "designated" so that it can recall the memory it was
assigned by boot firmware.

This also dovetails with the conversation I had with Paul Blinzer at
Plumbers about an ability to designate Soft Reserve memory. So a generic
facility to designate memory allows accelerators to recall their address
range if the decoders ever lose their configuration. It also tells the
rest of the CXL subsystem "hands off, this range was accelerator
designated by platform firmware".

[1]: http://lore.kernel.org/69b1e0aacb9d0_2132100c5@dwillia2-mobl4.notmuch