From edbbc60ed86f4b690838e6c4b0aed48803e334cc Mon Sep 17 00:00:00 2001 From: Jonathan Bell 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 --- 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);