Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption
From: Jan-Bernd Themann <hidden>
Date: 2008-09-15 12:17:37
Also in:
linux-rt-users, linuxppc-dev
Hi, we are a bit worried about putting this into the mainstream part of non real time linux. There interrupts work perfectly fine, and it was a bit of a challenge to get there for all cases / configurations / machines. Could you try to enable these changes only for RT-Linux via a real-time kconfig switch? This way we make sure we don't break the scheme for eHEA / eHCA. Regards, Jan-Bernd & Christoph Sebastien Dugue [off-list ref] wrote on 15.09.2008 10:04:06:
WARNING: HACK - HACK - HACK Under the RT kernel (with hardirq preemption) the eHEA driver hangs
right
after booting. Fiddling with the hardirqs and softirqs priorities allows
to
run a bit longer but as soon as the network gets under load, the hang returns. After investigating, it appears that the driver is loosing interrupts. To make a long story short, looking at the code, it appears that the
XICS
maps all its interrupts to level sensitive interrupts (I don't know if it's the reality or if it's due to an incomplete implementation - no datasheets available to check) and use the fasteoi processing flow. When entering the low level handler, level sensitive interrupts are
masked,
then eio'd in interrupt context and then unmasked at the end of hardirq processing. That's fine as any interrupt comming in-between will still be processed
since
the kernel replays those pending interrupts. However, it appears that the eHEA interrupts are behaving as edge
sensitive
interrupts and are routed through the XICS which process those as level sensitive using the fasteoi handler __OR__ the XICS loses interruptswhen
they
are masked. Therefore the masking done in the handler causes any interrupt happening while in the handler to be lost. So this patch maps the interrupts being requested through ibmebus_request_irq() as edge sensitive interrupts (this concerns both the eHEA and the eHCA - only users of ibmebus_request_irq()) and changes the way
edge
interrupts are processed by the fasteoi handler. It works for the eHEA, dunno for the eHCA. So, unless all the designers of the XICS & eHEA have been shot to keep
it
quoted hunk ↗ jump to hunk
a secret, could someone knowledgeable shed some light on this issue. Thanks, Sebastien. Not-Signed-off-by: Sebastien Dugue [off-list ref] --- arch/powerpc/kernel/ibmebus.c | 11 ++++++++++- kernel/irq/chip.c | 5 +++-- kernel/irq/manage.c | 9 ++++++--- 3 files changed, 19 insertions(+), 6 deletions(-)diff --git a/arch/powerpc/kernel/ibmebus.c
b/arch/powerpc/kernel/ibmebus.c
quoted hunk ↗ jump to hunk
index 9971159..5200323 100644--- a/arch/powerpc/kernel/ibmebus.c +++ b/arch/powerpc/kernel/ibmebus.c@@ -41,6 +41,7 @@ #include <linux/kobject.h> #include <linux/dma-mapping.h> #include <linux/interrupt.h> +#include <linux/irq.h> #include <linux/of.h> #include <linux/of_platform.h> #include <asm/ibmebus.h>@@ -213,11 +214,19 @@ int ibmebus_request_irq(u32 ist, irq_handler_t
handler,
quoted hunk ↗ jump to hunk
void *dev_id) { unsigned int irq = irq_create_mapping(NULL, ist); + struct irq_desc *desc; + int ret; if (irq == NO_IRQ) return -EINVAL; - return request_irq(irq, handler, irq_flags, devname, dev_id); + ret = request_irq(irq, handler, irq_flags, devname, dev_id); + + desc = irq_desc + irq; + desc->status &= ~(IRQ_TYPE_SENSE_MASK | IRQ_LEVEL); + desc->status |= IRQ_TYPE_EDGE_RISING; + + return ret; } EXPORT_SYMBOL(ibmebus_request_irq);diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c index b7b397a..6d366ca 100644 --- a/kernel/irq/chip.c +++ b/kernel/irq/chip.c@@ -430,7 +430,7 @@ handle_fasteoi_irq(unsigned int irq, structirq_desc *desc) action = desc->action; if (unlikely(!action || (desc->status & (IRQ_INPROGRESS | IRQ_DISABLED)))) { - desc->status |= IRQ_PENDING; + desc->status |= IRQ_PENDING | IRQ_MASKED; if (desc->chip->mask) desc->chip->mask(irq); goto out;@@ -439,9 +439,10 @@ handle_fasteoi_irq(unsigned int irq, structirq_desc *desc) desc->status |= IRQ_INPROGRESS; /* * In the threaded case we fall back to a mask+eoi sequence: + * excepted for edge interrupts which are not masked. */ if (redirect_hardirq(desc)) { - if (desc->chip->mask) + if (desc->chip->mask && !(desc->status & IRQ_TYPE_EDGE_BOTH)) desc->chip->mask(irq); goto out; }diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index 3bffa20..3e39c71 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c@@ -788,9 +788,12 @@ static void do_hardirq(struct irq_desc *desc) thread_simple_irq(desc); else if (desc->handle_irq == handle_level_irq) thread_level_irq(desc); - else if (desc->handle_irq == handle_fasteoi_irq) - thread_fasteoi_irq(desc); - else if (desc->handle_irq == handle_edge_irq) + else if (desc->handle_irq == handle_fasteoi_irq) { + if (desc->status & IRQ_TYPE_EDGE_BOTH) + thread_edge_irq(desc); + else + thread_fasteoi_irq(desc); + } else if (desc->handle_irq == handle_edge_irq) thread_edge_irq(desc); else thread_do_irq(desc);-- 1.6.0.1.308.gede4c