Messages in this thread | | | From | Eugeniy Paltsev <> | Subject | [BUG] ARCv2: MCIP: GFRC: mcip cmd/readback concurrency | Date | Thu, 22 Feb 2018 14:26:44 +0000 |
| |
To read any data from ARconnect we have special interface which includes two AUX registers: MCIP_CMD and MCIP_READBACK. We write command to MCIP_CMD and read data from MCIP_READBACK after that.
We have only one instance of this registers per cluster, so we need to held global lock before access them. This lock is defined in arch/arc/kernel/mcip.c
To read GFRC value we also use MCIP_CMD/MCIP_READBACK pair, but we take only local lock instead of global 'mcip_lock' lock:
---------->[drivers/clocksource/arc_timer.c]<---------- static u64 arc_read_gfrc(struct clocksource *cs) { unsigned long flags; u32 l, h;
local_irq_save(flags);
__mcip_cmd(CMD_GFRC_READ_LO, 0); l = read_aux_reg(ARC_REG_MCIP_READBACK);
__mcip_cmd(CMD_GFRC_READ_HI, 0); h = read_aux_reg(ARC_REG_MCIP_READBACK);
local_irq_restore(flags);
return (((u64)h) << 32) | l; } -------------------------->8---------------------------
So we can break any command (like inter core interrupt send) which uses MCIP_CMD/MCIP_READBACK pair when we read time from GFRC.
One possible solution is to create function like gfrc_read() in mcip.c which will use global 'mcip_lock' and call it from current 'arc_read_gfrc' function.
Or we can create a wrapper like 'mcip_read' in arch/arc/kernel/mcip.c with next functionality: ------->8-------- u32 mcip_read(u32 cmd) { u32 ret;
raw_spin_lock_irqsave(&mcip_lock);
__mcip_cmd(cmd, 0); ret = read_aux_reg(ARC_REG_MCIP_READBACK);
raw_spin_unlock_irqrestore(&mcip_lock);
return ret; } ------->8--------
-- Eugeniy Paltsev | |