usb: gadget: storage: make FSG_NUM_BUFFERS variable size

FSG_NUM_BUFFERS is set to 2 as default.
Usually 2 buffers are enough to establish a good buffering pipeline.
The number may be increased in order to compensate a for bursty VFS
behaviour.

Here follows a description of system that may require more than
2 buffers.
 * CPU ondemand governor active
 * latency cost for wake up and/or frequency change
 * DMA for IO

Use case description.
 * Data transfer from MMC via VFS to USB.
 * DMA shuffles data from MMC and to USB.
 * The CPU wakes up every now and then to pass data in and out from VFS,
   which cause the bursty VFS behaviour.

Test set up
 * Running dd on the host reading from the mass storage device
 * cmdline: dd if=/dev/sdb of=/dev/null bs=4k count=$((256*100))
 * Caches are dropped on the host and on the device before each run

Measurements on a Snowball board with ondemand_governor active.

FSG_NUM_BUFFERS 2
104857600 bytes (105 MB) copied, 5.62173 s, 18.7 MB/s
104857600 bytes (105 MB) copied, 5.61811 s, 18.7 MB/s
104857600 bytes (105 MB) copied, 5.57817 s, 18.8 MB/s

FSG_NUM_BUFFERS 4
104857600 bytes (105 MB) copied, 5.26839 s, 19.9 MB/s
104857600 bytes (105 MB) copied, 5.2691 s, 19.9 MB/s
104857600 bytes (105 MB) copied, 5.2711 s, 19.9 MB/s

There may not be one optimal number for all boards. This is why
the number is added to Kconfig. If selecting USB_GADGET_DEBUG_FILES
this value may be set by a module parameter as well.

Signed-off-by: Per Forlin <per.forlin@linaro.org>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>

1 files changed, 17 insertions, 10 deletions

diff --git a/drivers/usb/gadget/file_storage.c b/drivers/usb/gadget/file_storage.c
index c6f96a2b3110..4b9797d07a67 100644
--- a/drivers/usb/gadget/file_storage.c
+++ b/drivers/usb/gadget/file_storage.c
@@ -460,7 +460,6 @@ struct fsg_dev {
 
 	struct fsg_buffhd	*next_buffhd_to_fill;
 	struct fsg_buffhd	*next_buffhd_to_drain;
-	struct fsg_buffhd	buffhds[FSG_NUM_BUFFERS];
 
 	int			thread_wakeup_needed;
 	struct completion	thread_notifier;
@@ -487,6 +486,8 @@ struct fsg_dev {
 	unsigned int		nluns;
 	struct fsg_lun		*luns;
 	struct fsg_lun		*curlun;
+	/* Must be the last entry */
+	struct fsg_buffhd	buffhds[];
 };
 
 typedef void (*fsg_routine_t)(struct fsg_dev *);
@@ -2737,7 +2738,7 @@ static int do_set_interface(struct fsg_dev *fsg, int altsetting)
 
 reset:
 	/* Deallocate the requests */
-	for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+	for (i = 0; i < fsg_num_buffers; ++i) {
 		struct fsg_buffhd *bh = &fsg->buffhds[i];
 
 		if (bh->inreq) {
@@ -2798,7 +2799,7 @@ reset:
 	}
 
 	/* Allocate the requests */
-	for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+	for (i = 0; i < fsg_num_buffers; ++i) {
 		struct fsg_buffhd	*bh = &fsg->buffhds[i];
 
 		if ((rc = alloc_request(fsg, fsg->bulk_in, &bh->inreq)) != 0)
@@ -2894,7 +2895,7 @@ static void handle_exception(struct fsg_dev *fsg)
 	/* Cancel all the pending transfers */
 	if (fsg->intreq_busy)
 		usb_ep_dequeue(fsg->intr_in, fsg->intreq);
-	for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+	for (i = 0; i < fsg_num_buffers; ++i) {
 		bh = &fsg->buffhds[i];
 		if (bh->inreq_busy)
 			usb_ep_dequeue(fsg->bulk_in, bh->inreq);
@@ -2905,7 +2906,7 @@ static void handle_exception(struct fsg_dev *fsg)
 	/* Wait until everything is idle */
 	for (;;) {
 		num_active = fsg->intreq_busy;
-		for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+		for (i = 0; i < fsg_num_buffers; ++i) {
 			bh = &fsg->buffhds[i];
 			num_active += bh->inreq_busy + bh->outreq_busy;
 		}
@@ -2927,7 +2928,7 @@ static void handle_exception(struct fsg_dev *fsg)
 	 * state, and the exception.  Then invoke the handler. */
 	spin_lock_irq(&fsg->lock);
 
-	for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+	for (i = 0; i < fsg_num_buffers; ++i) {
 		bh = &fsg->buffhds[i];
 		bh->state = BUF_STATE_EMPTY;
 	}
@@ -3157,7 +3158,7 @@ static void /* __init_or_exit */ fsg_unbind(struct usb_gadget *gadget)
 	}
 
 	/* Free the data buffers */
-	for (i = 0; i < FSG_NUM_BUFFERS; ++i)
+	for (i = 0; i < fsg_num_buffers; ++i)
 		kfree(fsg->buffhds[i].buf);
 
 	/* Free the request and buffer for endpoint 0 */
@@ -3445,7 +3446,7 @@ static int __init fsg_bind(struct usb_gadget *gadget)
 	req->complete = ep0_complete;
 
 	/* Allocate the data buffers */
-	for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+	for (i = 0; i < fsg_num_buffers; ++i) {
 		struct fsg_buffhd	*bh = &fsg->buffhds[i];
 
 		/* Allocate for the bulk-in endpoint.  We assume that
@@ -3456,7 +3457,7 @@ static int __init fsg_bind(struct usb_gadget *gadget)
 			goto out;
 		bh->next = bh + 1;
 	}
-	fsg->buffhds[FSG_NUM_BUFFERS - 1].next = &fsg->buffhds[0];
+	fsg->buffhds[fsg_num_buffers - 1].next = &fsg->buffhds[0];
 
 	/* This should reflect the actual gadget power source */
 	usb_gadget_set_selfpowered(gadget);
@@ -3572,7 +3573,9 @@ static int __init fsg_alloc(void)
 {
 	struct fsg_dev		*fsg;
 
-	fsg = kzalloc(sizeof *fsg, GFP_KERNEL);
+	fsg = kzalloc(sizeof *fsg +
+		      fsg_num_buffers * sizeof *(fsg->buffhds), GFP_KERNEL);
+
 	if (!fsg)
 		return -ENOMEM;
 	spin_lock_init(&fsg->lock);
@@ -3590,6 +3593,10 @@ static int __init fsg_init(void)
 	int		rc;
 	struct fsg_dev	*fsg;
 
+	rc = fsg_num_buffers_validate();
+	if (rc != 0)
+		return rc;
+
 	if ((rc = fsg_alloc()) != 0)
 		return rc;
 	fsg = the_fsg;