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, 21 insertions, 8 deletions

diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index 4306a8339487..756941473148 100644
--- a/drivers/usb/gadget/f_mass_storage.c
+++ b/drivers/usb/gadget/f_mass_storage.c
@@ -362,7 +362,7 @@ struct fsg_common {
 
         struct fsg_buffhd       *next_buffhd_to_fill;
         struct fsg_buffhd       *next_buffhd_to_drain;
-        struct fsg_buffhd       buffhds[FSG_NUM_BUFFERS];
+        struct fsg_buffhd       *buffhds;
 
         int                     cmnd_size;
         u8                      cmnd[MAX_COMMAND_SIZE];
@@ -2340,7 +2340,7 @@ reset:
         if (common->fsg) {
                 fsg = common->fsg;
 
-                for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+                for (i = 0; i < fsg_num_buffers; ++i) {
                         struct fsg_buffhd *bh = &common->buffhds[i];
 
                         if (bh->inreq) {
@@ -2397,7 +2397,7 @@ reset:
         clear_bit(IGNORE_BULK_OUT, &fsg->atomic_bitflags);
 
         /* Allocate the requests */
-        for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+        for (i = 0; i < fsg_num_buffers; ++i) {
                 struct fsg_buffhd       *bh = &common->buffhds[i];
 
                 rc = alloc_request(common, fsg->bulk_in, &bh->inreq);
@@ -2466,7 +2466,7 @@ static void handle_exception(struct fsg_common *common)
 
         /* Cancel all the pending transfers */
         if (likely(common->fsg)) {
-                for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+                for (i = 0; i < fsg_num_buffers; ++i) {
                         bh = &common->buffhds[i];
                         if (bh->inreq_busy)
                                 usb_ep_dequeue(common->fsg->bulk_in, bh->inreq);
@@ -2478,7 +2478,7 @@ static void handle_exception(struct fsg_common *common)
                 /* Wait until everything is idle */
                 for (;;) {
                         int num_active = 0;
-                        for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+                        for (i = 0; i < fsg_num_buffers; ++i) {
                                 bh = &common->buffhds[i];
                                 num_active += bh->inreq_busy + bh->outreq_busy;
                         }
@@ -2501,7 +2501,7 @@ static void handle_exception(struct fsg_common *common)
          */
         spin_lock_irq(&common->lock);
 
-        for (i = 0; i < FSG_NUM_BUFFERS; ++i) {
+        for (i = 0; i < fsg_num_buffers; ++i) {
                 bh = &common->buffhds[i];
                 bh->state = BUF_STATE_EMPTY;
         }
@@ -2710,6 +2710,10 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common,
         int nluns, i, rc;
         char *pathbuf;
 
+        rc = fsg_num_buffers_validate();
+        if (rc != 0)
+                return ERR_PTR(rc);
+
         /* Find out how many LUNs there should be */
         nluns = cfg->nluns;
         if (nluns < 1 || nluns > FSG_MAX_LUNS) {
@@ -2728,6 +2732,14 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common,
                 common->free_storage_on_release = 0;
         }
 
+        common->buffhds = kcalloc(fsg_num_buffers,
+                                  sizeof *(common->buffhds), GFP_KERNEL);
+        if (!common->buffhds) {
+                if (common->free_storage_on_release)
+                        kfree(common);
+                return ERR_PTR(-ENOMEM);
+        }
+
         common->ops = cfg->ops;
         common->private_data = cfg->private_data;
 
@@ -2805,7 +2817,7 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common,
 
         /* Data buffers cyclic list */
         bh = common->buffhds;
-        i = FSG_NUM_BUFFERS;
+        i = fsg_num_buffers;
         goto buffhds_first_it;
         do {
                 bh->next = bh + 1;
@@ -2931,12 +2943,13 @@ static void fsg_common_release(struct kref *ref)
 
         {
                 struct fsg_buffhd *bh = common->buffhds;
-                unsigned i = FSG_NUM_BUFFERS;
+                unsigned i = fsg_num_buffers;
                 do {
                         kfree(bh->buf);
                 } while (++bh, --i);
         }
 
+        kfree(common->buffhds);
         if (common->free_storage_on_release)
                 kfree(common);
 }