[PATCH v2] irqchip/gicv3-its: Enable cacheable attribute Read-allocate hints

[Shanker Donthineni]

Read-allocation hints are not enabled for both the GIC-ITS and GICR
tables. This forces the hardware to always read the table contents
from an external memory (DDR) which is slow compared to cache memory.
Most of the tables are often read by hardware. So, it's better to
enable Read-allocate hints in addition to Write-allocate hints in
order to improve the GICR_PEND, GICR_PROP, Collection, Device, and
vCPU tables lookup time.

Signed-off-by: Shanker Donthineni <shankerd at codeaurora.org>
---
Implemented a test case to prove that enabling Read Allocation hints
improves ITS lookup time ~15% while delivering a LPI event. Used the
ITS command INV to analyze time spent in device, collection, prop and
pending table lookups.
  
Pseudo code:
    Create a fake ITS device.
    Record PMU cycle counter before sending INV command.
    Build and send ITS INT command.
         ITS hardware triggers device table lookup.
              ITTE table & collection table lookup.
          ITS property table lookup.
          ITS pending table lookup.
          Deliver interrupt to CPU interface.
    do_IRQ() called.
    Measure the total CPU cycle spent to reach this point. 

Without ReadAllocation hints:
/sys/kernel/debug # echo 100 > lpitest
[   94.693968] CPU[1] niter=100 cycles=0x8dfc0 avg=0x16b7 min=0x1652

With ReadAllocation hints:
/sys/kernel/debug # echo 100 > lpitest
[   98.617873] CPU[1] niter=100 cycles=0x7df49 avg=0x1427 min=0x1388

 drivers/irqchip/irq-gic-v3-its.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index c5dee30..227a1eb 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -961,7 +961,7 @@ static bool its_parse_baser_device(struct its_node *its, struct its_baser *baser
 				   u32 psz, u32 *order)
 {
 	u64 esz = GITS_BASER_ENTRY_SIZE(its_read_baser(its, baser));
-	u64 val = GITS_BASER_InnerShareable | GITS_BASER_WaWb;
+	u64 val = GITS_BASER_InnerShareable | GITS_BASER_RaWaWb;
 	u32 ids = its->device_ids;
 	u32 new_order = *order;
 	bool indirect = false;
@@ -1026,7 +1026,7 @@ static int its_alloc_tables(struct its_node *its)
 	u64 typer = gic_read_typer(its->base + GITS_TYPER);
 	u32 ids = GITS_TYPER_DEVBITS(typer);
 	u64 shr = GITS_BASER_InnerShareable;
-	u64 cache = GITS_BASER_WaWb;
+	u64 cache = GITS_BASER_RaWaWb;
 	u32 psz = SZ_64K;
 	int err, i;
 
@@ -1123,7 +1123,7 @@ static void its_cpu_init_lpis(void)
 	/* set PROPBASE */
 	val = (page_to_phys(gic_rdists->prop_page) |
 	       GICR_PROPBASER_InnerShareable |
-	       GICR_PROPBASER_WaWb |
+	       GICR_PROPBASER_RaWaWb |
 	       ((LPI_NRBITS - 1) & GICR_PROPBASER_IDBITS_MASK));
 
 	writeq_relaxed(val, rbase + GICR_PROPBASER);
@@ -1148,7 +1148,7 @@ static void its_cpu_init_lpis(void)
 	/* set PENDBASE */
 	val = (page_to_phys(pend_page) |
 	       GICR_PENDBASER_InnerShareable |
-	       GICR_PENDBASER_WaWb);
+	       GICR_PENDBASER_RaWaWb);
 
 	writeq_relaxed(val, rbase + GICR_PENDBASER);
 	tmp = readq_relaxed(rbase + GICR_PENDBASER);
@@ -1712,7 +1712,7 @@ static int __init its_probe_one(struct resource *res,
 		goto out_free_tables;
 
 	baser = (virt_to_phys(its->cmd_base)	|
-		 GITS_CBASER_WaWb		|
+		 GITS_CBASER_RaWaWb		|
 		 GITS_CBASER_InnerShareable	|
 		 (ITS_CMD_QUEUE_SZ / SZ_4K - 1)	|
 		 GITS_CBASER_VALID);
-- 
Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.