firewire: ohci: lazy bus time initialization

The Bus_Time CSR is virtually never used, so we can avoid burning CPU in
interrupt context for 1 or 3 IsochronousCycleTimer accesses every minute
by not tracking the bus time until the CSR is actually accessed for the
first time.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
index c1af05e834b610e98acba423c6e811239c9d908e..1c365b82781509fc35891d384d07ffdd45633526 100644 (file)
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -191,6 +191,7 @@ struct fw_ohci {
        unsigned quirks;
        unsigned int pri_req_max;
        u32 bus_time;
+       bool bus_time_running;
        bool is_root;
        bool csr_state_setclear_abdicate;
        int n_ir;
@@ -1726,6 +1727,13 @@ static u32 update_bus_time(struct fw_ohci *ohci)
 {
        u32 cycle_time_seconds = get_cycle_time(ohci) >> 25;
 
+       if (unlikely(!ohci->bus_time_running)) {
+               reg_write(ohci, OHCI1394_IntMaskSet, OHCI1394_cycle64Seconds);
+               ohci->bus_time = (lower_32_bits(get_seconds()) & ~0x7f) |
+                                (cycle_time_seconds & 0x40);
+               ohci->bus_time_running = true;
+       }
+
        if ((ohci->bus_time & 0x40) != (cycle_time_seconds & 0x40))
                ohci->bus_time += 0x40;
 
@@ -2213,7 +2221,7 @@ static int ohci_enable(struct fw_card *card,
 {
        struct fw_ohci *ohci = fw_ohci(card);
        struct pci_dev *dev = to_pci_dev(card->device);
-       u32 lps, seconds, version, irqs;
+       u32 lps, version, irqs;
        int i, ret;
 
        if (software_reset(ohci)) {
@@ -2269,9 +2277,7 @@ static int ohci_enable(struct fw_card *card,
                  (OHCI1394_MAX_PHYS_RESP_RETRIES << 8) |
                  (200 << 16));
 
-       seconds = lower_32_bits(get_seconds());
-       reg_write(ohci, OHCI1394_IsochronousCycleTimer, seconds << 25);
-       ohci->bus_time = seconds & ~0x3f;
+       ohci->bus_time_running = false;
 
        version = reg_read(ohci, OHCI1394_Version) & 0x00ff00ff;
        if (version >= OHCI_VERSION_1_1) {
@@ -2369,7 +2375,6 @@ static int ohci_enable(struct fw_card *card,
                OHCI1394_postedWriteErr |
                OHCI1394_selfIDComplete |
                OHCI1394_regAccessFail |
-               OHCI1394_cycle64Seconds |
                OHCI1394_cycleInconsistent |
                OHCI1394_unrecoverableError |
                OHCI1394_cycleTooLong |
@@ -2658,7 +2663,8 @@ static void ohci_write_csr(struct fw_card *card, int csr_offset, u32 value)
 
        case CSR_BUS_TIME:
                spin_lock_irqsave(&ohci->lock, flags);
-               ohci->bus_time = (ohci->bus_time & 0x7f) | (value & ~0x7f);
+               ohci->bus_time = (update_bus_time(ohci) & 0x40) |
+                                (value & ~0x7f);
                spin_unlock_irqrestore(&ohci->lock, flags);
                break;