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| author | Mike Isely <isely@pobox.com> | 2008-08-30 13:09:31 -0500 |
|---|---|---|
| committer | Mike Isely <isely@pobox.com> | 2008-08-30 13:09:31 -0500 |
| commit | 1072381235b9397551ff19c608a25b47ef5c7994 (patch) | |
| tree | d01189f98d2824d669509e02e755608bde693c59 | |
| parent | fe9b8beb1f13deceb3f0b1f38e1704ee33e31a91 (diff) | |
| download | mediapointer-dvb-s2-1072381235b9397551ff19c608a25b47ef5c7994.tar.gz mediapointer-dvb-s2-1072381235b9397551ff19c608a25b47ef5c7994.tar.bz2 | |
pvrusb2: Add comment elaborating on direct use of swab32()
From: Mike Isely <isely@pobox.com>
Priority: normal
Signed-off-by: Mike Isely <isely@pobox.com>
| -rw-r--r-- | linux/drivers/media/video/pvrusb2/pvrusb2-hdw.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/linux/drivers/media/video/pvrusb2/pvrusb2-hdw.c b/linux/drivers/media/video/pvrusb2/pvrusb2-hdw.c index 881610b60..70ed24e9a 100644 --- a/linux/drivers/media/video/pvrusb2/pvrusb2-hdw.c +++ b/linux/drivers/media/video/pvrusb2/pvrusb2-hdw.c @@ -1323,6 +1323,17 @@ 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]); |