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Commit 4a9bde9b authored by Stefan Richter's avatar Stefan Richter
Browse files

firewire: get_cycle_timer optimization and cleanup 



ohci:  Break out of the retry loop if too many attempts were necessary.
This may theoretically happen if the chip is fatally defective or if the
get_cycle_timer ioctl was performed after a CardBus controller was
ejected.

Also micro-optimize the loop by re-using the last two register reads in
the next iteration, remove a questionable inline keyword, and shuffle a
comment around.

core:  ioctl_get_cycle_timer() is always called with interrupts on,
therefore local_irq_save() can be replaced by local_irq_disable().
Disabled local IRQs imply disabled preemption, hence preempt_disable()
can be removed.

Signed-off-by: default avatarStefan Richter <stefanr@s5r6.in-berlin.de>
parent 1c1517ef

drivers/firewire/core-cdev.c

+7 −9
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ 
#include <linux/firewire.h>

#include <linux/firewire-cdev.h>

#include <linux/idr.h>

#include <linux/irqflags.h>

#include <linux/jiffies.h>

#include <linux/kernel.h>

#include <linux/kref.h>
@@ -32,7 +33,6 @@ 
#include <linux/module.h>

#include <linux/mutex.h>

#include <linux/poll.h>

#include <linux/preempt.h>

#include <linux/sched.h>

#include <linux/spinlock.h>

#include <linux/time.h>
@@ -1013,21 +1013,19 @@ static int ioctl_get_cycle_timer(struct client *client, void *buffer) 
{

	struct fw_cdev_get_cycle_timer *request = buffer;

	struct fw_card *card = client->device->card;

	unsigned long long bus_time;

	struct timeval tv;

	unsigned long flags;

	u32 cycle_time;



	preempt_disable();

	local_irq_save(flags);

	local_irq_disable();



	bus_time = card->driver->get_bus_time(card);

	cycle_time = card->driver->get_bus_time(card);

	do_gettimeofday(&tv);



	local_irq_restore(flags);

	preempt_enable();

	local_irq_enable();



	request->local_time = tv.tv_sec * 1000000ULL + tv.tv_usec;

	request->cycle_timer = bus_time & 0xffffffff;

	request->cycle_timer = cycle_time;



	return 0;

}

drivers/firewire/ohci.c

+29 −28
Original line number Diff line number Diff line
@@ -1795,60 +1795,61 @@ static int ohci_enable_phys_dma(struct fw_card *card, 
#endif /* CONFIG_FIREWIRE_OHCI_REMOTE_DMA */

}



static inline u32 cycle_timer_ticks(u32 cycle_timer)

static u32 cycle_timer_ticks(u32 cycle_timer)

{

	u32 ticks;



	ticks = cycle_timer & 0xfff;

	ticks += 3072 * ((cycle_timer >> 12) & 0x1fff);

	ticks += (3072 * 8000) * (cycle_timer >> 25);



	return ticks;

}



/*

 * Some controllers exhibit one or more of the following bugs when updating the

 * iso cycle timer register:

 *  - When the lowest six bits are wrapping around to zero, a read that happens

 *    at the same time will return garbage in the lowest ten bits.

 *  - When the cycleOffset field wraps around to zero, the cycleCount field is

 *    not incremented for about 60 ns.

 *  - Occasionally, the entire register reads zero.

 *

 * To catch these, we read the register three times and ensure that the

 * difference between each two consecutive reads is approximately the same, i.e.

 * less than twice the other.  Furthermore, any negative difference indicates an

 * error.  (A PCI read should take at least 20 ticks of the 24.576 MHz timer to

 * execute, so we have enough precision to compute the ratio of the differences.)

 */

static u64 ohci_get_bus_time(struct fw_card *card)

{

	struct fw_ohci *ohci = fw_ohci(card);

	u32 c0, c1, c2;

	u32 t0, t1, t2;

	s32 diff01, diff12;

	u64 bus_time;

	int i;



	if (!ohci->iso_cycle_timer_quirk) {

	c2 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);

	} else {

		/*

		 * Some controllers exhibit one or more of the following bugs

		 * when updating the iso cycle timer register:

		 *  - When the lowest six bits are wrapping around to zero,

		 *    a read that happens at the same time will return garbage

		 *    in the lowest ten bits.

		 *  - When the cycleOffset field wraps around to zero, the

		 *    cycleCount field is not incremented for about 60 ns.

		 *  - Occasionally, the entire register reads zero.

		 *

		 * To catch these, we read the register three times and ensure

		 * that the difference between each two consecutive reads is

		 * approximately the same, i.e., less than twice the other.

		 * Furthermore, any negative difference indicates an error.

		 * (A PCI read should take at least 20 ticks of the 24.576 MHz

		 * timer to execute, so we have enough precision to compute the

		 * ratio of the differences.)

		 */



	if (ohci->iso_cycle_timer_quirk) {

		i = 0;

		c1 = c2;

		c2 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);

		do {

			c0 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);

			c1 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);

			c0 = c1;

			c1 = c2;

			c2 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);

			t0 = cycle_timer_ticks(c0);

			t1 = cycle_timer_ticks(c1);

			t2 = cycle_timer_ticks(c2);

			diff01 = t1 - t0;

			diff12 = t2 - t1;

		} while (diff01 <= 0 || diff12 <= 0 ||

			 diff01 / diff12 >= 2 || diff12 / diff01 >= 2);

		} while ((diff01 <= 0 || diff12 <= 0 ||

			  diff01 / diff12 >= 2 || diff12 / diff01 >= 2)

			 && i++ < 20);

	}

	bus_time = ((u64)atomic_read(&ohci->bus_seconds) << 32) | c2;



	return bus_time;

	return ((u64)atomic_read(&ohci->bus_seconds) << 32) | c2;

}



static void copy_iso_headers(struct iso_context *ctx, void *p)