summaryrefslogtreecommitdiffstats
path: root/drivers/usb/gadget/storage_common.c
diff options
context:
space:
mode:
authorPer Forlin <per.forlin@linaro.org>2011-08-19 21:21:27 +0200
committerFelipe Balbi <balbi@ti.com>2011-09-09 13:06:04 +0300
commit6532c7fdb2c3a2ec1b949ecd2ff5375069c1639a (patch)
tree26afd8fdff7923f818f49aa405bb4208d1da914e /drivers/usb/gadget/storage_common.c
parent04eee25b1d754a837360504b7af426d1f86ffeb7 (diff)
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>
Diffstat (limited to 'drivers/usb/gadget/storage_common.c')
-rw-r--r--drivers/usb/gadget/storage_common.c33
1 files changed, 31 insertions, 2 deletions
diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c
index 3ea70d8549e..9fd37999860 100644
--- a/drivers/usb/gadget/storage_common.c
+++ b/drivers/usb/gadget/storage_common.c
@@ -52,6 +52,12 @@
* characters rather then a pointer to void.
*/
+/*
+ * When USB_GADGET_DEBUG_FILES is defined the module param num_buffers
+ * sets the number of pipeline buffers (length of the fsg_buffhd array).
+ * The valid range of num_buffers is: num >= 2 && num <= 4.
+ */
+
#include <linux/usb/storage.h>
#include <scsi/scsi.h>
@@ -264,8 +270,31 @@ static struct fsg_lun *fsg_lun_from_dev(struct device *dev)
#define EP0_BUFSIZE 256
#define DELAYED_STATUS (EP0_BUFSIZE + 999) /* An impossibly large value */
-/* Number of buffers we will use. 2 is enough for double-buffering */
-#define FSG_NUM_BUFFERS 2
+#ifdef CONFIG_USB_GADGET_DEBUG_FILES
+
+static unsigned int fsg_num_buffers = CONFIG_USB_GADGET_STORAGE_NUM_BUFFERS;
+module_param_named(num_buffers, fsg_num_buffers, uint, S_IRUGO);
+MODULE_PARM_DESC(num_buffers, "Number of pipeline buffers");
+
+#else
+
+/*
+ * Number of buffers we will use.
+ * 2 is usually enough for good buffering pipeline
+ */
+#define fsg_num_buffers CONFIG_USB_GADGET_STORAGE_NUM_BUFFERS
+
+#endif /* CONFIG_USB_DEBUG */
+
+/* check if fsg_num_buffers is within a valid range */
+static inline int fsg_num_buffers_validate(void)
+{
+ if (fsg_num_buffers >= 2 && fsg_num_buffers <= 4)
+ return 0;
+ pr_err("fsg_num_buffers %u is out of range (%d to %d)\n",
+ fsg_num_buffers, 2 ,4);
+ return -EINVAL;
+}
/* Default size of buffer length. */
#define FSG_BUFLEN ((u32)16384)