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

On Fri, 2018-03-23 at 17:17 +0100, christophe lombard wrote:

Le 23/03/2018 à 03:14, Benjamin Herrenschmidt a écrit :

quoted

On Thu, 2018-03-22 at 17:37 +0100, Christophe Lombard wrote:

quoted

The cxl driver cannot disable the interrupt at the device level and has
to use disable_irq[_nosync] instead.
To avoid the implementation of the lazy optimisation (the interrupt is
marked disabled, but the hardware is left unmasked), we can disable it,
for a particular irq line, by calling
'irq_set_status_flags(irq, IRQ_DISABLE_UNLAZY)'.

Why do you need that ? What's wrong with the lazy approach ? It makes
disable_irq/enable_irq faster...

You shouldn't need that unless your device is generating a *LOT* of
irqs while disabled.

An issue on POWERVM (CAPI) has been introduced with the following patch
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bf22ff45bed664aefb5c4e43029057a199b7070c 

The PSL or AFU interrupts are never received by the cxl driver because 
the interrupts are never unmasked.

Without this patch (genirq: Avoid unnecessary low level irq function 
calls), the callback desc->irq_data.chip->irq_unmask(&desc->irq_data); 
(= ics_rtas_unmask_irq()) is called by default through irq_enable().

I don't see why this would change with the patch... 

The cxl driver disables the interrupts before attaching the process 
element and enables the interrupts after that.

How ? Using disable_irq or something else ?

In the current code, irq_enable() unmasks the irq only if the irq state 
is IRQD_IRQ_MASKED but it does not.

Sorry I don't really parse your sentence. You mean there's a disconnect
between the "HW" (or pHyp) state of the interrupt and the
IRQD_IRQ_MASKED flag ? That shouldn't happen... if that's the case the
bug is elsewhere, what is causing the disconnect in the first place ?

Call irq_set_status_flags(irq, IRQ_DISABLE_UNLAZY) allows forcing 
irq_disable() to update the irq state to IRQD_IRQ_MASKED and by default
irq_enable() will unmask the irq through ics_rtas_unmask_irq().

Hrm. I don't quite understand. You shouldn't need that, I suspect you
are papering over a different bug but I'm not 100% certain as I don't
completely understand what's happening.

Cheers,
Ben.

quoted

quoted

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);
  		}
  	}