Re: [RFC PATCH 28/33] irqchip/gic-v3-its: Support VPE doorbell invalidation even when !DirectLPI

[Shanker Donthineni]

Hi Marc,


On 01/17/2017 04:20 AM, Marc Zyngier wrote:

When we don't have the DirectLPI feature, we must work around the
architecture shortcomings to be able to perform the required
invalidation.

For this, we create a fake device whose sole purpose is to
provide a way to issue a map/inv/unmap sequence (and the corresponding
sync operations). That's 6 commands and a full serialization point
to be able to do this.

You just have hope the hypervisor won't do that too often...

Signed-off-by: Marc Zyngier 
---
  drivers/irqchip/irq-gic-v3-its.c | 59
++--
  1 file changed, 57 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c
b/drivers/irqchip/irq-gic-v3-its.c
index 008fb71..3787579 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -133,6 +133,9 @@ struct its_device {
u32 device_id;
  };
  
+static struct its_device *vpe_proxy_dev;

+static DEFINE_RAW_SPINLOCK(vpe_proxy_dev_lock);
+
  static LIST_HEAD(its_nodes);
  static DEFINE_SPINLOCK(its_lock);
  static struct rdists *gic_rdists;
@@ -993,8 +996,35 @@ static void lpi_update_config(struct irq_data *d, u8
clr, u8 set)
struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
void __iomem *rdbase;
  
-		rdbase = per_cpu_ptr(gic_rdists->rdist,

vpe->col_idx)->rd_base;
-   writeq_relaxed(d->hwirq, rdbase + GICR_INVLPIR);
+   if (gic_rdists->has_direct_lpi) {
+   rdbase = per_cpu_ptr(gic_rdists->rdist,
vpe->col_idx)->rd_base;
+   writeq_relaxed(d->hwirq, rdbase + GICR_INVLPIR);
+   } else {
+   /*
+* This is insane.
+*
+* If a GICv4 doesn't implement Direct LPIs,
+* the only way to perform an invalidate is to
+* use a fake device to issue a MAP/INV/UNMAP
+* sequence. Since each of these commands has
+* a sync operation, this is really fast. Not.
+*
+* We always use event 0, and this serialize
+* all VPE invalidations in the system.
+*
+* Broken by design(tm).
+*/
+   unsigned long flags;
+
+   raw_spin_lock_irqsave(_proxy_dev_lock, flags);
+
+   vpe_proxy_dev->event_map.col_map[0] =
vpe->col_idx;
+   its_send_mapvi(vpe_proxy_dev, vpe->vpe_db_lpi, 0);
+   its_send_inv(vpe_proxy_dev, 0);
+   its_send_discard(vpe_proxy_dev, 0);
+
+   raw_spin_unlock_irqrestore(_proxy_dev_lock,
flags);
+   }
}
  }
  
@@ -2481,6 +2511,31 @@ static struct irq_domain *its_init_vpe_domain(void)

struct fwnode_handle *handle;
struct irq_domain *domain;
  
+	if (gic_rdists->has_direct_lpi) {

+   pr_info("ITS: Using DirectLPI for VPE invalidation\n");
+   } else {
+   struct its_node *its;
+
+   list_for_each_entry(its, _nodes, entry) {
+   u32 devid;
+
+   if (!its->is_v4)
+   continue;
+
+   /* Use the last possible DevID */
+   devid = GENMASK(its->device_ids - 1, 0);
How do we know this 'devid' is not being used by real hardware devices? 
I think we need some kind check in its_msi_prepare() to skip this device 
or WARN.

Unfortunately Qualcomm doesn't support Direct LPI feature.


--
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux 
Foundation Collaborative Project.

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Re: [RFC PATCH 28/33] irqchip/gic-v3-its: Support VPE doorbell invalidation even when !DirectLPI

[Thomas Gleixner]

On Tue, 17 Jan 2017, Marc Zyngier wrote:
> When we don't have the DirectLPI feature, we must work around the
> architecture shortcomings to be able to perform the required
> invalidation.
> 
> For this, we create a fake device whose sole purpose is to
> provide a way to issue a map/inv/unmap sequence (and the corresponding
> sync operations). That's 6 commands and a full serialization point
> to be able to do this.
> 
> You just have hope the hypervisor won't do that too often...
> 
> Signed-off-by: Marc Zyngier 

Reviewed-by: Thomas Gleixner 
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