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Subject[PATCH] USB: f_mass_storage: dynamic buffers for better alignment
From: Michal Nazarewicz <mina86@mina86.com>

Using of "static" buffers in fsg_buffhd structure causes buffers
not to be aligned to any bigger power of two (like cache size for
instance) which as a result may lead to some copying of data or
slower DMA access (as head must to be copied via CPU). So even
though code gets a bit more complicated this patch changes the
behaviour of mass storage function to use kmalloc()ed buffers which
are (because of their size) page aligned -- that should be enought
for any DMA or other hardware.
---
drivers/usb/gadget/f_mass_storage.c | 23 ++++++++++++++++++-----
1 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index 84f6491..eff339d 100644
--- a/drivers/usb/gadget/f_mass_storage.c
+++ b/drivers/usb/gadget/f_mass_storage.c
@@ -302,7 +302,6 @@ static const char fsg_string_interface[] = "Mass Storage";


#define FSG_NO_INTR_EP 1
-#define FSG_BUFFHD_STATIC_BUFFER 1
#define FSG_NO_DEVICE_STRINGS 1
#define FSG_NO_OTG 1
#define FSG_NO_INTR_EP 1
@@ -2747,13 +2746,19 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common,


/* Data buffers cyclic list */
- /* Buffers in buffhds are static -- no need for additional
- * allocation. */
bh = common->buffhds;
- i = FSG_NUM_BUFFERS - 1;
+ i = FSG_NUM_BUFFERS;
+ goto buffhds_first_it;
do {
bh->next = bh + 1;
- } while (++bh, --i);
+ ++bh;
+buffhds_first_it:
+ bh->buf = kmalloc(FSG_BUFLEN, GFP_KERNEL);
+ if (unlikely(!bh->buf)) {
+ rc = -ENOMEM;
+ goto error_release;
+ }
+ } while (--i);
bh->next = common->buffhds;


@@ -2861,6 +2866,7 @@ static void fsg_common_release(struct kref *ref)
container_of(ref, struct fsg_common, ref);
unsigned i = common->nluns;
struct fsg_lun *lun = common->luns;
+ struct fsg_buffhd *bh;

/* If the thread isn't already dead, tell it to exit now */
if (common->state != FSG_STATE_TERMINATED) {
@@ -2882,6 +2888,13 @@ static void fsg_common_release(struct kref *ref)
}

kfree(common->luns);
+
+ i = FSG_BUFFHD;
+ bh = common->buffhds;
+ do {
+ kfree(bh->buf);
+ } while (++bh, --i);
+
if (common->free_storage_on_release)
kfree(common);
}
--
1.7.0


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