[PATCH] cxl: disable the lazy approach for irqs in POWERVM environment.

[Benjamin Herrenschmidt]

On Mon, 2018-05-07 at 18:02 +0200, christophe lombard wrote:
> 
> To answer to your questions, here is the timeline in the cxl driver
> 
>    1. call disable_irq()
> 
>    2. call plpar_hcall9() to attach a process element
> 	During this phase, phyp (as described in CAPI PAPR document) 	
> 	disables the virtual interrupts provided in the process-element-
> 	struct.
> 	Then the partition must use ibm,set-xive to enable the virtual
> 	interrupt source after H_ATTACH_CA_PROCESS completes
> 	successfully.

Ok, this is the breakage. This PAPR API is badly defined, nothing other
than the existing interrupt management PAPR calls should affect the
enable/disable state of the interrupt The fact that attaching a process
element does is a broken design.

>    3. call enable_irq()
> 	Before the following patch (genirq: Avoid unnecessary low level
> 	irq function calls) be pushed in mainline, the unmask api
> 	(= ics_rtas_unmask_irq()) was called by default and everything
> 	was ok.
> 
> 	With this patch, the unmask api is now called only if 		
> 	IRQD_IRQ_MASKED is set and in our case, it's never done and the
> 	irqs remain masked.
> 
> 
>    So, there is a disconnect between the 'HW' (phyp) state of the
>    interrupt and the IRQD_IRQ_MASKED flag.
> 
>    In the timeline of the cxl driver, the IRQD_IRQ_MASKED flag is never
>    set.
>    This flag was not used in enable_irq(), before that the patch "genirq:
>    Avoid ..." was pushed. So ics_rtas_unmask_irq() was called and
>    everything was ok.
> 
> Thanks
> 
> > > 
> > > 
> > > 
> > > > > Signed-off-by: Christophe Lombard <clombard at linux.vnet.ibm.com>
> > > > > ---
> > > > >    drivers/misc/cxl/guest.c | 1 +
> > > > >    1 file changed, 1 insertion(+)
> > > > > 
> > > > > diff --git a/drivers/misc/cxl/guest.c b/drivers/misc/cxl/guest.c
> > > > > index f58b4b6c..dc476e1 100644
> > > > > --- a/drivers/misc/cxl/guest.c
> > > > > +++ b/drivers/misc/cxl/guest.c
> > > > > @@ -389,6 +389,7 @@ static void disable_afu_irqs(struct cxl_context *ctx)
> > > > >    		hwirq = ctx->irqs.offset[r];
> > > > >    		for (i = 0; i < ctx->irqs.range[r]; hwirq++, i++) {
> > > > >    			virq = irq_find_mapping(NULL, hwirq);
> > > > > +			irq_set_status_flags(virq, IRQ_DISABLE_UNLAZY);
> > > > >    			disable_irq(virq);
> > > > >    		}
> > > > >    	}