[PATCH RFT v2 8/8] media: hantro: jpeg: Remove open-coded size in quantization table code

[Chen-Yu Tsai]

The quantization tables used in the Hantro JPEG encoder driver are
implicitly sized by the data they contain, but the loop that scales
the tables based on the compression quality hard codes the size to
64. No code exists to check whether the two actually match.

Commit 85bdcb7eaae7 ("media: hantro: Write the quantization tables in
proper order") introduced two new tables, with sizes hardcoded to 64,
but still no checking if all the sizes are the same.

Commit 41479adb5e52 ("media: hantro: Avoid global variable for jpeg
quantization tables") added the macro JPEG_QUANT_SIZE, but only the
newly added fields used this.

This has resulted in code scattered with magic numbers and array sizes
that happen to match up, without any sort of sanity checking to enforce
it.

Drop the hard-coded array sizes, replace the magic loop count with
a proper JPEG_QUANT_SIZE macro, and add BUILD_BUG_ON()s to check
that all the table sizes match up.

Signed-off-by: Chen-Yu Tsai <wenst at chromium.org>
---
 drivers/staging/media/hantro/hantro_jpeg.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/media/hantro/hantro_jpeg.c b/drivers/staging/media/hantro/hantro_jpeg.c
index 84d3f0bfff00..d07b1b449b61 100644
--- a/drivers/staging/media/hantro/hantro_jpeg.c
+++ b/drivers/staging/media/hantro/hantro_jpeg.c
@@ -49,7 +49,7 @@ static const unsigned char chroma_q_table[] = {
 	0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63, 0x63
 };
 
-static const unsigned char zigzag[64] = {
+static const unsigned char zigzag[] = {
 	 0,  1,  8, 16,  9,  2,  3, 10,
 	17, 24, 32, 25, 18, 11,  4,  5,
 	12, 19, 26, 33, 40, 48, 41, 34,
@@ -60,7 +60,7 @@ static const unsigned char zigzag[64] = {
 	53, 60, 61, 54, 47, 55, 62, 63
 };
 
-static const u32 hw_reorder[64] = {
+static const u32 hw_reorder[] = {
 	 0,  8, 16, 24,  1,  9, 17, 25,
 	32, 40, 48, 56, 33, 41, 49, 57,
 	 2, 10, 18, 26,  3, 11, 19, 27,
@@ -292,7 +292,10 @@ jpeg_scale_quant_table(unsigned char *file_q_tab,
 {
 	int i;
 
-	for (i = 0; i < 64; i++) {
+	BUILD_BUG_ON(ARRAY_SIZE(zigzag) != JPEG_QUANT_SIZE);
+	BUILD_BUG_ON(ARRAY_SIZE(hw_reorder) != JPEG_QUANT_SIZE);
+
+	for (i = 0; i < JPEG_QUANT_SIZE; i++) {
 		file_q_tab[i] = jpeg_scale_qp(tab[zigzag[i]], scale);
 		reordered_q_tab[i] = jpeg_scale_qp(tab[hw_reorder[i]], scale);
 	}
@@ -311,6 +314,11 @@ static void jpeg_set_quality(struct hantro_jpeg_ctx *ctx)
 	else
 		scale = 200 - 2 * ctx->quality;
 
+	BUILD_BUG_ON(ARRAY_SIZE(luma_q_table) != JPEG_QUANT_SIZE);
+	BUILD_BUG_ON(ARRAY_SIZE(chroma_q_table) != JPEG_QUANT_SIZE);
+	BUILD_BUG_ON(ARRAY_SIZE(ctx->hw_luma_qtable) != JPEG_QUANT_SIZE);
+	BUILD_BUG_ON(ARRAY_SIZE(ctx->hw_chroma_qtable) != JPEG_QUANT_SIZE);
+
 	jpeg_scale_quant_table(ctx->buffer + LUMA_QUANT_OFF,
 			       ctx->hw_luma_qtable, luma_q_table, scale);
 	jpeg_scale_quant_table(ctx->buffer + CHROMA_QUANT_OFF,
-- 
2.34.1.575.g55b058a8bb-goog