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Subject[PATCH 37/71] ncr5380: Standardize work queueing algorithm
The complex main_running/queue_main mechanism is peculiar to
atari_NCR5380.c. It isn't SMP safe and offers little value given that
the work queue already offers concurrency management. Remove this
complexity to bring atari_NCR5380.c closer to NCR5380.c.

It is not a good idea to call the information transfer state machine from
queuecommand because, according to Documentation/scsi/scsi_mid_low_api.txt
that could happen in soft irq context. Fix this.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>

---
drivers/scsi/NCR5380.h | 1
drivers/scsi/atari_NCR5380.c | 80 +++----------------------------------------
2 files changed, 6 insertions(+), 75 deletions(-)

Index: linux/drivers/scsi/NCR5380.h
===================================================================
--- linux.orig/drivers/scsi/NCR5380.h 2015-11-18 19:33:49.000000000 +1100
+++ linux/drivers/scsi/NCR5380.h 2015-11-18 19:33:51.000000000 +1100
@@ -262,7 +262,6 @@ struct NCR5380_hostdata {
* transfer to handle chip overruns */
int retain_dma_intr;
struct work_struct main_task;
- volatile int main_running;
#ifdef SUPPORT_TAGS
struct tag_alloc TagAlloc[8][8]; /* 8 targets and 8 LUNs */
#endif
Index: linux/drivers/scsi/atari_NCR5380.c
===================================================================
--- linux.orig/drivers/scsi/atari_NCR5380.c 2015-11-18 19:33:48.000000000 +1100
+++ linux/drivers/scsi/atari_NCR5380.c 2015-11-18 19:33:51.000000000 +1100
@@ -611,36 +611,6 @@ static void NCR5380_print_phase(struct S

#endif

-/*
- * ++roman: New scheme of calling NCR5380_main()
- *
- * If we're not in an interrupt, we can call our main directly, it cannot be
- * already running. Else, we queue it on a task queue, if not 'main_running'
- * tells us that a lower level is already executing it. This way,
- * 'main_running' needs not be protected in a special way.
- *
- * queue_main() is a utility function for putting our main onto the task
- * queue, if main_running is false. It should be called only from a
- * interrupt or bottom half.
- */
-
-#include <linux/gfp.h>
-#include <linux/workqueue.h>
-#include <linux/interrupt.h>
-
-static inline void queue_main(struct NCR5380_hostdata *hostdata)
-{
- if (!hostdata->main_running) {
- /* If in interrupt and NCR5380_main() not already running,
- queue it on the 'immediate' task queue, to be processed
- immediately after the current interrupt processing has
- finished. */
- queue_work(hostdata->work_q, &hostdata->main_task);
- }
- /* else: nothing to do: the running NCR5380_main() will pick up
- any newly queued command. */
-}
-
/**
* NCR58380_info - report driver and host information
* @instance: relevant scsi host instance
@@ -723,8 +693,6 @@ static void __maybe_unused NCR5380_print
hostdata = (struct NCR5380_hostdata *)instance->hostdata;

local_irq_save(flags);
- printk("NCR5380: coroutine is%s running.\n",
- hostdata->main_running ? "" : "n't");
if (!hostdata->connected)
printk("scsi%d: no currently connected command\n", HOSTNO);
else
@@ -766,8 +734,6 @@ static int __maybe_unused NCR5380_show_i
hostdata = (struct NCR5380_hostdata *)instance->hostdata;

local_irq_save(flags);
- seq_printf(m, "NCR5380: coroutine is%s running.\n",
- hostdata->main_running ? "" : "n't");
if (!hostdata->connected)
seq_printf(m, "scsi%d: no currently connected command\n", HOSTNO);
else
@@ -991,17 +957,8 @@ static int NCR5380_queue_command(struct
dprintk(NDEBUG_QUEUES, "scsi%d: command added to %s of queue\n", H_NO(cmd),
(cmd->cmnd[0] == REQUEST_SENSE) ? "head" : "tail");

- /* If queue_command() is called from an interrupt (real one or bottom
- * half), we let queue_main() do the job of taking care about main. If it
- * is already running, this is a no-op, else main will be queued.
- *
- * If we're not in an interrupt, we can call NCR5380_main()
- * unconditionally, because it cannot be already running.
- */
- if (in_interrupt() || irqs_disabled())
- queue_main(hostdata);
- else
- NCR5380_main(&hostdata->main_task);
+ /* Kick off command processing */
+ queue_work(hostdata->work_q, &hostdata->main_task);
return 0;
}

@@ -1038,30 +995,11 @@ static void NCR5380_main(struct work_str
unsigned long flags;

/*
- * We run (with interrupts disabled) until we're sure that none of
- * the host adapters have anything that can be done, at which point
- * we set main_running to 0 and exit.
- *
- * Interrupts are enabled before doing various other internal
- * instructions, after we've decided that we need to run through
- * the loop again.
- *
- * this should prevent any race conditions.
- *
* ++roman: Just disabling the NCR interrupt isn't sufficient here,
* because also a timer int can trigger an abort or reset, which can
* alter queues and touch the Falcon lock.
*/

- /* Tell int handlers main() is now already executing. Note that
- no races are possible here. If an int comes in before
- 'main_running' is set here, and queues/executes main via the
- task queue, it doesn't do any harm, just this instance of main
- won't find any work left to do. */
- if (hostdata->main_running)
- return;
- hostdata->main_running = 1;
-
local_save_flags(flags);
do {
local_irq_disable(); /* Freeze request queues */
@@ -1176,11 +1114,6 @@ static void NCR5380_main(struct work_str
done = 0;
}
} while (!done);
-
- /* Better allow ints _after_ 'main_running' has been cleared, else
- an interrupt could believe we'll pick up the work it left for
- us, but we won't see it anymore here... */
- hostdata->main_running = 0;
local_irq_restore(flags);
}

@@ -1293,6 +1226,7 @@ static void NCR5380_dma_complete(struct
static irqreturn_t NCR5380_intr(int irq, void *dev_id)
{
struct Scsi_Host *instance = dev_id;
+ struct NCR5380_hostdata *hostdata = shost_priv(instance);
int done = 1, handled = 0;
unsigned char basr;

@@ -1361,11 +1295,9 @@ static irqreturn_t NCR5380_intr(int irq,
#endif
}

- if (!done) {
- dprintk(NDEBUG_INTR, "scsi%d: in int routine, calling main\n", HOSTNO);
- /* Put a call to NCR5380_main() on the queue... */
- queue_main(shost_priv(instance));
- }
+ if (!done)
+ queue_work(hostdata->work_q, &hostdata->main_task);
+
return IRQ_RETVAL(handled);
}




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