linux-kernel - [PATCH v6 1/6] media: dvb-frontends: tda10048: Make the range of z explicit.

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Message-Id: <20250111-fix-cocci-v6-1-1aa7842006cc@chromium.org>
Date: Sat, 11 Jan 2025 09:55:14 +0000
From: Ricardo Ribalda <ribalda@...omium.org>
To: Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Stanimir Varbanov <stanimir.k.varbanov@...il.com>, 
 Vikash Garodia <quic_vgarodia@...cinc.com>, 
 Bryan O'Donoghue <bryan.odonoghue@...aro.org>, 
 Hans Verkuil <hverkuil@...all.nl>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-arm-msm@...r.kernel.org, Kosta Stefanov <costa.stephanoff@...il.com>, 
 Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH v6 1/6] media: dvb-frontends: tda10048: Make the range of z
 explicit.

The datasheet recommends 55MHz frequency sampling, with a max of 69 MHz.
(Kudos to Kosta Stefanov for the calculations).

Replace z with a 32 bit uint, and make the range of the variable
explicit.

Found by cocci:
drivers/media/dvb-frontends/tda10048.c:345:1-7: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.

Reviewed-by: Kosta Stefanov <costa.stephanoff@...il.com>
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
 drivers/media/dvb-frontends/tda10048.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/media/dvb-frontends/tda10048.c b/drivers/media/dvb-frontends/tda10048.c
index 3e725cdcc66b..1f87eb0dcf2a 100644
--- a/drivers/media/dvb-frontends/tda10048.c
+++ b/drivers/media/dvb-frontends/tda10048.c
@@ -328,7 +328,8 @@ static int tda10048_set_wref(struct dvb_frontend *fe, u32 sample_freq_hz,
 			     u32 bw)
 {
 	struct tda10048_state *state = fe->demodulator_priv;
-	u64 t, z;
+	u64 t;
+	u32 z;

 	dprintk(1, "%s()\n", __func__);

@@ -341,6 +342,11 @@ static int tda10048_set_wref(struct dvb_frontend *fe, u32 sample_freq_hz,
 	/* t *= 2147483648 on 32bit platforms */
 	t *= (2048 * 1024);
 	t *= 1024;
+
+	/*
+	 * Sample frequency is typically 55 MHz, with a theoretical maximum of
+	 * 69 MHz. With a 32 bit z we have enough accuracy for up to 613 MHz.
+	 */
 	z = 7 * sample_freq_hz;
 	do_div(t, z);
 	t += 5;

-- 
2.47.1.613.gc27f4b7a9f-goog