diff options
| author | Mike Isely <isely@pobox.com> | 2008-08-30 15:09:31 -0300 |
|---|---|---|
| committer | Mauro Carvalho Chehab <mchehab@redhat.com> | 2008-10-12 09:36:57 -0200 |
| commit | 5f33df1443cd53283279d017b45ed1b1bc66f622 (patch) | |
| tree | 49a4fc26ff01fd0a9e5834a07f043c52fbad153c /drivers/media/video/pvrusb2/pvrusb2-hdw.c | |
| parent | 83512e207479d0bdb83ee1e000a306af9e6e870e (diff) | |
V4L/DVB (8893): pvrusb2: Add comment elaborating on direct use of swab32()
Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Diffstat (limited to 'drivers/media/video/pvrusb2/pvrusb2-hdw.c')
| -rw-r--r-- | drivers/media/video/pvrusb2/pvrusb2-hdw.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/drivers/media/video/pvrusb2/pvrusb2-hdw.c b/drivers/media/video/pvrusb2/pvrusb2-hdw.c index 7fa903ad26b..c8dedbab6e3 100644 --- a/drivers/media/video/pvrusb2/pvrusb2-hdw.c +++ b/drivers/media/video/pvrusb2/pvrusb2-hdw.c @@ -1313,6 +1313,17 @@ int pvr2_upload_firmware2(struct pvr2_hdw *hdw) if (bcnt > FIRMWARE_CHUNK_SIZE) bcnt = FIRMWARE_CHUNK_SIZE; memcpy(fw_ptr, fw_entry->data + fw_done, bcnt); /* Usbsnoop log shows that we must swap bytes... */ + /* Some background info: The data being swapped here is a + firmware image destined for the mpeg encoder chip that + lives at the other end of a USB endpoint. The encoder + chip always talks in 32 bit chunks and its storage is + organized into 32 bit words. However from the file + system to the encoder chip everything is purely a byte + stream. The firmware file's contents are always 32 bit + swapped from what the encoder expects. Thus the need + always exists to swap the bytes regardless of the endian + type of the host processor and therefore swab32() makes + the most sense. */ for (icnt = 0; icnt < bcnt/4 ; icnt++) ((u32 *)fw_ptr)[icnt] = swab32(((u32 *)fw_ptr)[icnt]); |