linux-kernel - [PATCH] media: vidtv: adjust signal strength range

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Message-Id: <c824a8b556280747c2a278864920baf8f78089ab.1600089788.git.mchehab+huawei@kernel.org>
Date:   Mon, 14 Sep 2020 15:23:10 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "Daniel W. S. Almeida" <dwlsalmeida@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: [PATCH] media: vidtv: adjust signal strength range

On real devices, signal strength is always a negative
number when represented in dBm. A more interesting
range is to use dBmV (which is what Kaffeine does,
for example). The conversion from the two units are
simple:

	dBmV = dBm - 108

Usually, signal strength ranges up to 100dBmV. Adjust the
maximum value to be around 74 dBmV, when there's no
frequency shift, which represents a good signal.

With that, Kaffeine displays it a lot better.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
---
 drivers/media/test-drivers/vidtv/vidtv_demod.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/media/test-drivers/vidtv/vidtv_demod.c b/drivers/media/test-drivers/vidtv/vidtv_demod.c
index c54c88cac84f..c825842758f0 100644
--- a/drivers/media/test-drivers/vidtv/vidtv_demod.c
+++ b/drivers/media/test-drivers/vidtv/vidtv_demod.c
@@ -181,12 +181,18 @@ static void vidtv_demod_update_stats(struct dvb_frontend *fe)
 	c->block_count.stat[0].scale = scale;
 
 	/*
-	 * Add a 0.5% of randomness at the signal streangth and CNR,
+	 * Add a 0.5% of randomness at the signal strength and CNR,
 	 * and make them different, as we want to have something closer
 	 * to a real case scenario.
+	 *
+	 * Also, usually, signal strength is a negative number in dBm.
 	 */
-	c->strength.stat[0].svalue = state->tuner_cnr + prandom_u32_max(state->tuner_cnr / 50);
-	c->cnr.stat[0].svalue = state->tuner_cnr - prandom_u32_max(state->tuner_cnr / 50);
+	c->strength.stat[0].svalue = state->tuner_cnr;
+	c->strength.stat[0].svalue -= prandom_u32_max(state->tuner_cnr / 50);
+	c->strength.stat[0].svalue -= 68000; /* Adjust to a better range */
+
+	c->cnr.stat[0].svalue = state->tuner_cnr;
+	c->cnr.stat[0].svalue -= prandom_u32_max(state->tuner_cnr / 50);
 
 }
 
-- 
2.26.2