diff options
Diffstat (limited to 'drivers/scsi/atari_scsi.c')
| -rw-r--r-- | drivers/scsi/atari_scsi.c | 83 |
1 files changed, 22 insertions, 61 deletions
diff --git a/drivers/scsi/atari_scsi.c b/drivers/scsi/atari_scsi.c index 65af08139787..a59ad94ea52b 100644 --- a/drivers/scsi/atari_scsi.c +++ b/drivers/scsi/atari_scsi.c @@ -14,55 +14,23 @@ * */ - -/**************************************************************************/ -/* */ -/* Notes for Falcon SCSI: */ -/* ---------------------- */ -/* */ -/* Since the Falcon SCSI uses the ST-DMA chip, that is shared among */ -/* several device drivers, locking and unlocking the access to this */ -/* chip is required. But locking is not possible from an interrupt, */ -/* since it puts the process to sleep if the lock is not available. */ -/* This prevents "late" locking of the DMA chip, i.e. locking it just */ -/* before using it, since in case of disconnection-reconnection */ -/* commands, the DMA is started from the reselection interrupt. */ -/* */ -/* Two possible schemes for ST-DMA-locking would be: */ -/* 1) The lock is taken for each command separately and disconnecting */ -/* is forbidden (i.e. can_queue = 1). */ -/* 2) The DMA chip is locked when the first command comes in and */ -/* released when the last command is finished and all queues are */ -/* empty. */ -/* The first alternative would result in bad performance, since the */ -/* interleaving of commands would not be used. The second is unfair to */ -/* other drivers using the ST-DMA, because the queues will seldom be */ -/* totally empty if there is a lot of disk traffic. */ -/* */ -/* For this reasons I decided to employ a more elaborate scheme: */ -/* - First, we give up the lock every time we can (for fairness), this */ -/* means every time a command finishes and there are no other commands */ -/* on the disconnected queue. */ -/* - If there are others waiting to lock the DMA chip, we stop */ -/* issuing commands, i.e. moving them onto the issue queue. */ -/* Because of that, the disconnected queue will run empty in a */ -/* while. Instead we go to sleep on a 'fairness_queue'. */ -/* - If the lock is released, all processes waiting on the fairness */ -/* queue will be woken. The first of them tries to re-lock the DMA, */ -/* the others wait for the first to finish this task. After that, */ -/* they can all run on and do their commands... */ -/* This sounds complicated (and it is it :-(), but it seems to be a */ -/* good compromise between fairness and performance: As long as no one */ -/* else wants to work with the ST-DMA chip, SCSI can go along as */ -/* usual. If now someone else comes, this behaviour is changed to a */ -/* "fairness mode": just already initiated commands are finished and */ -/* then the lock is released. The other one waiting will probably win */ -/* the race for locking the DMA, since it was waiting for longer. And */ -/* after it has finished, SCSI can go ahead again. Finally: I hope I */ -/* have not produced any deadlock possibilities! */ -/* */ -/**************************************************************************/ - +/* + * Notes for Falcon SCSI DMA + * + * The 5380 device is one of several that all share the DMA chip. Hence + * "locking" and "unlocking" access to this chip is required. + * + * Two possible schemes for ST DMA acquisition by atari_scsi are: + * 1) The lock is taken for each command separately (i.e. can_queue == 1). + * 2) The lock is taken when the first command arrives and released + * when the last command is finished (i.e. can_queue > 1). + * + * The first alternative limits SCSI bus utilization, since interleaving + * commands is not possible. The second gives better performance but is + * unfair to other drivers needing to use the ST DMA chip. In order to + * allow the IDE and floppy drivers equal access to the ST DMA chip + * the default is can_queue == 1. + */ #include <linux/module.h> #include <linux/types.h> @@ -443,6 +411,10 @@ static int falcon_get_lock(struct Scsi_Host *instance) if (IS_A_TT()) return 1; + if (stdma_is_locked_by(scsi_falcon_intr) && + instance->hostt->can_queue > 1) + return 1; + if (in_interrupt()) return stdma_try_lock(scsi_falcon_intr, instance); @@ -776,22 +748,11 @@ static int __init atari_scsi_probe(struct platform_device *pdev) atari_scsi_reg_write = atari_scsi_falcon_reg_write; } - /* The values for CMD_PER_LUN and CAN_QUEUE are somehow arbitrary. - * Higher values should work, too; try it! - * (But cmd_per_lun costs memory!) - * - * But there seems to be a bug somewhere that requires CAN_QUEUE to be - * 2*CMD_PER_LUN. At least on a TT, no spurious timeouts seen since - * changed CMD_PER_LUN... - * - * Note: The Falcon currently uses 8/1 setting due to unsolved problems - * with cmd_per_lun != 1 - */ if (ATARIHW_PRESENT(TT_SCSI)) { atari_scsi_template.can_queue = 16; atari_scsi_template.sg_tablesize = SG_ALL; } else { - atari_scsi_template.can_queue = 8; + atari_scsi_template.can_queue = 1; atari_scsi_template.sg_tablesize = SG_NONE; } |