sfc: Fix timekeeping in efx_mcdi_poll()

efx_mcdi_poll() uses get_seconds() to read the current time and to
implement a polling timeout.  The use of this function was chosen
partly because it could easily be replaced in a co-sim environment
with a macro that read the simulated time.

Unfortunately the real get_seconds() returns the system time (real
time) which is subject to adjustment by e.g. ntpd.  If the system time
is adjusted forward during a polled MCDI operation, the effective
timeout can be shorter than the intended 10 seconds, resulting in a
spurious failure.  It is also possible for a backward adjustment to
delay detection of a areal failure.

Use jiffies instead, and change MCDI_RPC_TIMEOUT to be denominated in
jiffies.  Also correct rounding of the timeout: check time > finish
(or rather time_after(time, finish)) and not time >= finish.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

diff --git a/drivers/net/ethernet/sfc/mcdi.c b/drivers/net/ethernet/sfc/mcdi.c
index 3ef71a0f99a8689a9a99006fa4053ad5aa23dc97..0095ce95150b9915b59cfea2344519879ca63ee5 100644 (file)
--- a/drivers/net/ethernet/sfc/mcdi.c
+++ b/drivers/net/ethernet/sfc/mcdi.c
@@ -22,7 +22,7 @@
  **************************************************************************
  */
 
-#define MCDI_RPC_TIMEOUT       10 /*seconds */
+#define MCDI_RPC_TIMEOUT       (10 * HZ)
 
 #define MCDI_PDU(efx)                                                  \
        (efx_port_num(efx) ? MC_SMEM_P1_PDU_OFST : MC_SMEM_P0_PDU_OFST)
@@ -120,7 +120,7 @@ static void efx_mcdi_copyout(struct efx_nic *efx, u8 *outbuf, size_t outlen)
 static int efx_mcdi_poll(struct efx_nic *efx)
 {
        struct efx_mcdi_iface *mcdi = efx_mcdi(efx);
-       unsigned int time, finish;
+       unsigned long time, finish;
        unsigned int respseq, respcmd, error;
        unsigned int pdu = FR_CZ_MC_TREG_SMEM + MCDI_PDU(efx);
        unsigned int rc, spins;
@@ -136,7 +136,7 @@ static int efx_mcdi_poll(struct efx_nic *efx)
         * and poll once a jiffy (approximately)
         */
        spins = TICK_USEC;
-       finish = get_seconds() + MCDI_RPC_TIMEOUT;
+       finish = jiffies + MCDI_RPC_TIMEOUT;
 
        while (1) {
                if (spins != 0) {
@@ -146,7 +146,7 @@ static int efx_mcdi_poll(struct efx_nic *efx)
                        schedule_timeout_uninterruptible(1);
                }
 
-               time = get_seconds();
+               time = jiffies;
 
                rmb();
                efx_readd(efx, &reg, pdu);
@@ -158,7 +158,7 @@ static int efx_mcdi_poll(struct efx_nic *efx)
                    EFX_DWORD_FIELD(reg, MCDI_HEADER_RESPONSE))
                        break;
 
-               if (time >= finish)
+               if (time_after(time, finish))
                        return -ETIMEDOUT;
        }
 
@@ -257,7 +257,7 @@ static int efx_mcdi_await_completion(struct efx_nic *efx)
        if (wait_event_timeout(
                    mcdi->wq,
                    atomic_read(&mcdi->state) == MCDI_STATE_COMPLETED,
-                   msecs_to_jiffies(MCDI_RPC_TIMEOUT * 1000)) == 0)
+                   MCDI_RPC_TIMEOUT) == 0)
                return -ETIMEDOUT;
 
        /* Check if efx_mcdi_set_mode() switched us back to polled completions.