xen: arm: allow platform code to select dom0 event channel irq

Currently the hardcoded use of GUEST_EVTCHN_PPI is problematic if that is a
real PPI on the platform.

We really need to be smarter about selecting an unused PPI but in the meantime
we can at least give the platform code the option of hardcoding a number which
works for the platform.

Hardcode a suitable PPI on the Xgene platform.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>

xen/arch/arm/domain.c

@@ -31,6 +31,7 @@
 #include <asm/processor-ca15.h>
 
 #include <asm/gic.h>
+#include <asm/platform.h>
 #include "vtimer.h"
 #include "vuart.h"
 
@@ -526,8 +527,10 @@ int arch_domain_create(struct domain *d, unsigned int domcr_flags)
     if ( (rc = vcpu_domain_init(d)) != 0 )
         goto fail;
 
-    /* XXX dom0 needs more intelligent selection of PPI */
-    d->arch.evtchn_irq = GUEST_EVTCHN_PPI;
+    if ( d->domain_id )
+        d->arch.evtchn_irq = GUEST_EVTCHN_PPI;
+    else
+        d->arch.evtchn_irq = platform_dom0_evtchn_ppi();
 
     /*
      * Virtual UART is only used by linux early printk and decompress code.

xen/arch/arm/platform.c

@@ -156,6 +156,13 @@ bool_t platform_device_is_blacklisted(const struct dt_device_node *node)
     return dt_match_node(blacklist, node);
 }
 
+unsigned int platform_dom0_evtchn_ppi(void)
+{
+    if ( platform && platform->dom0_evtchn_ppi )
+        return platform->dom0_evtchn_ppi;
+    return GUEST_EVTCHN_PPI;
+}
+
 /*
  * Local variables:
  * mode: C

xen/arch/arm/platforms/xgene-storm.c

@@ -36,6 +36,7 @@ static const char * const xgene_storm_dt_compat[] __initconst =
 PLATFORM_START(xgene_storm, "APM X-GENE STORM")
     .compatible = xgene_storm_dt_compat,
     .quirks = xgene_storm_quirks,
+    .dom0_evtchn_ppi = 24,
 PLATFORM_END
 
 /*

xen/include/asm-arm/platform.h

@@ -37,6 +37,10 @@ struct platform_desc {
      * List of devices which must not pass-through to a guest
      */
     const struct dt_device_match *blacklist_dev;
+    /*
+     * The IRQ (PPI) to use to inject event channels to dom0.
+     */
+    unsigned int dom0_evtchn_ppi;
 };
 
 /*
@@ -61,6 +65,7 @@ void platform_reset(void);
 void platform_poweroff(void);
 bool_t platform_has_quirk(uint32_t quirk);
 bool_t platform_device_is_blacklisted(const struct dt_device_node *node);
+unsigned int platform_dom0_evtchn_ppi(void);
 
 #define PLATFORM_START(_name, _namestr)                         \
 static const struct platform_desc  __plat_desc_##_name __used   \