[Skiboot] [PATCH] xive: disable store EOI support

[Cédric Le Goater]

Hardware has limitations which would require to put a sync after each
store EOI to make sure the MMIO operations that change the ESB state
are ordered. This is a killer for performance and the PHBs do not
support the sync. So remove the store EOI for the moment, until
hardware is improved.

Signed-off-by: Cédric Le Goater <clg at kaod.org>
---
 hw/xive.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/hw/xive.c b/hw/xive.c
index 468e5b0446e9..01913768118f 100644
--- a/hw/xive.c
+++ b/hw/xive.c
@@ -486,6 +486,10 @@ struct xive {
 	void		*q_ovf;
 };
 
+#define XIVE_STORE_EOI_ENABLED 0
+#define XIVE_CAN_STORE_EOI(x) \
+	(XIVE_STORE_EOI_ENABLED && ((x)->rev >= XIVE_REV_2))
+
 /* Global DT node */
 static struct dt_node *xive_dt_node;
 
@@ -1750,7 +1754,11 @@ static bool xive_config_init(struct xive *x)
 
 	/* Enable StoreEOI */
 	val = xive_regr(x, VC_SBC_CONFIG);
-	val |= VC_SBC_CONF_CPLX_CIST | VC_SBC_CONF_CIST_BOTH;
+	if (XIVE_CAN_STORE_EOI(x))
+		val |= VC_SBC_CONF_CPLX_CIST | VC_SBC_CONF_CIST_BOTH;
+	else
+		xive_dbg(x, "store EOI is disabled\n");
+
 	val |= VC_SBC_CONF_NO_UPD_PRF;
 	xive_regw(x, VC_SBC_CONFIG, val);
 
@@ -2790,7 +2798,7 @@ void xive_register_ipi_source(uint32_t base, uint32_t count, void *data,
 	assert(s);
 
 	/* Store EOI supported on DD2.0 */
-	if (x->rev >= XIVE_REV_2)
+	if (XIVE_CAN_STORE_EOI(x))
 		flags |= XIVE_SRC_STORE_EOI;
 
 	/* Callbacks assume the MMIO base corresponds to the first
@@ -2898,7 +2906,7 @@ static struct xive *init_one_xive(struct dt_node *np)
 
 	/* Register built-in source controllers (aka IPIs) */
 	flags = XIVE_SRC_EOI_PAGE1 | XIVE_SRC_TRIGGER_PAGE;
-	if (x->rev >= XIVE_REV_2)
+	if (XIVE_CAN_STORE_EOI(x))
 		flags |= XIVE_SRC_STORE_EOI;
 	__xive_register_source(x, &x->ipis, x->int_base,
 			       x->int_hw_bot - x->int_base, IPI_ESB_SHIFT,
-- 
2.13.6