openwrt/target/linux/bcm27xx/patches-5.4/950-0386-dwc_otg-fiq_fsm-add-a-barrier-on-entry-into-FIQ-hand.patch

From edbbc60ed86f4b690838e6c4b0aed48803e334cc Mon Sep 17 00:00:00 2001
From: Jonathan Bell <jonathan@raspberrypi.org>
Date: Mon, 13 Jan 2020 15:54:55 +0000
Subject: [PATCH] dwc_otg: fiq_fsm: add a barrier on entry into FIQ
 handler(s)

On BCM2835, there is no hardware guarantee that multiple outstanding
reads to different peripherals will complete in-order. The FIQ code
uses peripheral reads without barriers for performance, so in the case
where a read to a slow peripheral was issued immediately prior to FIQ
entry, the first peripheral read that the FIQ did could end up with
wrong read data returned.

Add dsb(sy) on entry so that all outstanding reads are retired.

The FIQ only issues reads to the dwc_otg core, so per-read barriers
in the handler itself are not required.

On BCM2836 and BCM2837 the barrier is not strictly required due to
differences in how the peripheral bus is implemented, but having
arch-specific handlers that introduce different latencies is risky.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.org>
---
 drivers/usb/host/dwc_otg/dwc_otg_fiq_fsm.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/usb/host/dwc_otg/dwc_otg_fiq_fsm.c
+++ b/drivers/usb/host/dwc_otg/dwc_otg_fiq_fsm.c
@@ -1259,6 +1259,9 @@ void notrace dwc_otg_fiq_fsm(struct fiq_
 	haintmsk_data_t haintmsk;
 	int kick_irq = 0;
 
+	/* Ensure peripheral reads issued prior to FIQ entry are complete */
+	dsb(sy);
+
 	gintsts_handled.d32 = 0;
 	haint_handled.d32 = 0;
 
@@ -1379,6 +1382,9 @@ void notrace dwc_otg_fiq_nop(struct fiq_
 	gintmsk_data_t gintmsk;
 	hfnum_data_t hfnum;
 
+	/* Ensure peripheral reads issued prior to FIQ entry are complete */
+	dsb(sy);
+
 	fiq_fsm_spin_lock(&state->lock);
 	hfnum.d32 = FIQ_READ(state->dwc_regs_base + HFNUM);
 	gintsts.d32 = FIQ_READ(state->dwc_regs_base + GINTSTS);