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

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

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Signed-off-by: Christophe Lombard <redacted>
---
   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);
   		}
   	}