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Subject[PATCH RFT v2 5/8] media: hantro: jpeg: Add COM segment to JPEG header to align image scan
Date
The JPEG header size is not 64-bit aligned. This makes the driver
require a bounce buffer for the encoded JPEG image scan output.

Add a COM (comment) segment to the JPEG header so that the header size
is a multiple of 64 bits. This will then allow dropping the use of the
bounce buffer, and instead have the hardware write out to the capture
buffer directly.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
drivers/staging/media/hantro/hantro_jpeg.c | 23 +++++++++++++++++++++-
drivers/staging/media/hantro/hantro_jpeg.h | 2 +-
2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/media/hantro/hantro_jpeg.c b/drivers/staging/media/hantro/hantro_jpeg.c
index 7d4018bd6876..e63eeef3952d 100644
--- a/drivers/staging/media/hantro/hantro_jpeg.c
+++ b/drivers/staging/media/hantro/hantro_jpeg.c
@@ -6,6 +6,9 @@
* Copyright (C) Jean-Francois Moine (http://moinejf.free.fr)
* Copyright (C) 2014 Philipp Zabel, Pengutronix
*/
+
+#include <linux/align.h>
+#include <linux/build_bug.h>
#include <linux/dma-mapping.h>
#include <linux/kernel.h>
#include <linux/string.h>
@@ -140,7 +143,7 @@ static const unsigned char chroma_ac_table[] = {
* and we'll use fixed offsets to change the width, height
* quantization tables, etc.
*/
-static const unsigned char hantro_jpeg_header[JPEG_HEADER_SIZE] = {
+static const unsigned char hantro_jpeg_header[] = {
/* SOI */
0xff, 0xd8,

@@ -247,11 +250,29 @@ static const unsigned char hantro_jpeg_header[JPEG_HEADER_SIZE] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

+ /* COM */
+ 0xff, 0xfe, 0x00, 0x03, 0x00,
+
/* SOS */
0xff, 0xda, 0x00, 0x0c, 0x03, 0x01, 0x00, 0x02,
0x11, 0x03, 0x11, 0x00, 0x3f, 0x00,
};

+/*
+ * JPEG_HEADER_SIZE is used in other parts of the driver in lieu of
+ * "sizeof(hantro_jpeg_header)". The two must be equal.
+ */
+static_assert(sizeof(hantro_jpeg_header) == JPEG_HEADER_SIZE);
+
+/*
+ * hantro_jpeg_header is padded with a COM segment, so that the payload
+ * of the SOS segment (the entropy-encoded image scan), which should
+ * trail the whole header, is 8-byte aligned for the hardware to write
+ * to directly.
+ */
+static_assert(IS_ALIGNED(sizeof(hantro_jpeg_header), 8),
+ "Hantro JPEG header size needs to be 8-byte aligned.");
+
static unsigned char jpeg_scale_qp(const unsigned char qp, int scale)
{
unsigned int temp;
diff --git a/drivers/staging/media/hantro/hantro_jpeg.h b/drivers/staging/media/hantro/hantro_jpeg.h
index f33c492134e4..0b49d0b82caa 100644
--- a/drivers/staging/media/hantro/hantro_jpeg.h
+++ b/drivers/staging/media/hantro/hantro_jpeg.h
@@ -1,6 +1,6 @@
/* SPDX-License-Identifier: GPL-2.0+ */

-#define JPEG_HEADER_SIZE 619
+#define JPEG_HEADER_SIZE 624
#define JPEG_QUANT_SIZE 64

struct hantro_jpeg_ctx {
--
2.34.1.575.g55b058a8bb-goog
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