linux-kernel - [PATCH] st-delta: avoid excessive stack usage

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Message-Id: <20250610093201.2645325-1-arnd@kernel.org>
Date: Tue, 10 Jun 2025 11:31:56 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Hugues Fruchet <hugues.fruchet@...s.st.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Peter Griffin <peter.griffin@...aro.org>
Cc: Arnd Bergmann <arnd@...db.de>,
	linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] st-delta: avoid excessive stack usage

From: Arnd Bergmann <arnd@...db.de>

Building with a reduced stack warning limit shows that delta_mjpeg_decode()
copies a giant structure to the stack each time but only uses three of
its members:

drivers/media/platform/st/sti/delta/delta-mjpeg-dec.c: In function 'delta_mjpeg_decode':
drivers/media/platform/st/sti/delta/delta-mjpeg-dec.c:427:1: error: the frame size of 1296 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]

Open-code the passing of the structure members that are actually used here.

Fixes: 433ff5b4a29b ("[media] st-delta: add mjpeg support")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 .../platform/st/sti/delta/delta-mjpeg-dec.c   | 20 ++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/media/platform/st/sti/delta/delta-mjpeg-dec.c b/drivers/media/platform/st/sti/delta/delta-mjpeg-dec.c
index 0533d4a083d2..a078f1107300 100644
--- a/drivers/media/platform/st/sti/delta/delta-mjpeg-dec.c
+++ b/drivers/media/platform/st/sti/delta/delta-mjpeg-dec.c
@@ -239,7 +239,7 @@ static int delta_mjpeg_ipc_open(struct delta_ctx *pctx)
 	return 0;
 }
 
-static int delta_mjpeg_ipc_decode(struct delta_ctx *pctx, struct delta_au *au)
+static int delta_mjpeg_ipc_decode(struct delta_ctx *pctx, dma_addr_t pstart, dma_addr_t pend)
 {
 	struct delta_dev *delta = pctx->dev;
 	struct delta_mjpeg_ctx *ctx = to_ctx(pctx);
@@ -256,8 +256,8 @@ static int delta_mjpeg_ipc_decode(struct delta_ctx *pctx, struct delta_au *au)
 
 	memset(params, 0, sizeof(*params));
 
-	params->picture_start_addr_p = (u32)(au->paddr);
-	params->picture_end_addr_p = (u32)(au->paddr + au->size - 1);
+	params->picture_start_addr_p = pstart;
+	params->picture_end_addr_p = pend;
 
 	/*
 	 * !WARNING!
@@ -374,12 +374,14 @@ static int delta_mjpeg_decode(struct delta_ctx *pctx, struct delta_au *pau)
 	struct delta_dev *delta = pctx->dev;
 	struct delta_mjpeg_ctx *ctx = to_ctx(pctx);
 	int ret;
-	struct delta_au au = *pau;
+	void *au_vaddr = pau->vaddr;
+	dma_addr_t au_dma = pau->paddr;
+	size_t au_size = pau->size;
 	unsigned int data_offset = 0;
 	struct mjpeg_header *header = &ctx->header_struct;
 
 	if (!ctx->header) {
-		ret = delta_mjpeg_read_header(pctx, au.vaddr, au.size,
+		ret = delta_mjpeg_read_header(pctx, au_vaddr, au_size,
 					      header, &data_offset);
 		if (ret) {
 			pctx->stream_errors++;
@@ -405,17 +407,17 @@ static int delta_mjpeg_decode(struct delta_ctx *pctx, struct delta_au *pau)
 			goto err;
 	}
 
-	ret = delta_mjpeg_read_header(pctx, au.vaddr, au.size,
+	ret = delta_mjpeg_read_header(pctx, au_vaddr, au_size,
 				      ctx->header, &data_offset);
 	if (ret) {
 		pctx->stream_errors++;
 		goto err;
 	}
 
-	au.paddr += data_offset;
-	au.vaddr += data_offset;
+	au_dma += data_offset;
+	au_vaddr += data_offset;
 
-	ret = delta_mjpeg_ipc_decode(pctx, &au);
+	ret = delta_mjpeg_ipc_decode(pctx, au_dma, au_dma + au_size - 1);
 	if (ret)
 		goto err;
 
-- 
2.39.5