linux-kernel - [PATCH v8 3/3] media: rcar-csi2: Optimize the selection PHTW register

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Date:   Thu, 18 Jun 2020 19:34:32 +0900
From:   Suresh Udipi <sudipi@...adit-jv.com>
To:     <mrodin@...adit-jv.com>
CC:     <akiyama@...-osk.co.jp>, <efriedrich@...adit-jv.com>,
        <erosca@...adit-jv.com>, <linux-kernel@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>,
        <mchehab@...nel.org>, <michael@...in.online>,
        <niklas.soderlund@...natech.se>, <securitycheck@...so.co.jp>,
        <sudipi@...adit-jv.com>
Subject: [PATCH v8 3/3] media: rcar-csi2: Optimize the selection PHTW register

PHTW register is selected based on default bit rate from Table[1].
for the bit rates less than or equal to 250. Currently first
value of default bit rate which is greater than or equal to
the caculated mbps is selected.This selection can be further
improved by selecting the default bit rate which is nearest to
the calculated value.

[1] specs r19uh0105ej0200-r-car-3rd-generation.pdf [Table 25.12]

Fixes: 769afd212b16 ("media: rcar-csi2: add Renesas R-Car MIPI CSI-2 receiver driver")

Signed-off-by: Suresh Udipi <sudipi@...adit-jv.com>
Signed-off-by: Michael Rodin <mrodin@...adit-jv.com>
---
 drivers/media/platform/rcar-vin/rcar-csi2.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c b/drivers/media/platform/rcar-vin/rcar-csi2.c
index 1184527..d7bf59f 100644
--- a/drivers/media/platform/rcar-vin/rcar-csi2.c
+++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
@@ -917,10 +917,18 @@ static int rcsi2_phtw_write_mbps(struct rcar_csi2 *priv, unsigned int mbps,
 				 const struct rcsi2_mbps_reg *values, u16 code)
 {
 	const struct rcsi2_mbps_reg *value;
+	const struct rcsi2_mbps_reg *prev_value = NULL;
 
-	for (value = values; value->mbps; value++)
+	for (value = values; value->mbps; value++) {
 		if (value->mbps >= mbps)
 			break;
+		prev_value = value;
+	}
+
+	if (prev_value &&
+	    ((mbps - prev_value->mbps) <= (value->mbps - mbps)))
+		value = prev_value;
+
 
 	if (!value->mbps) {
 		dev_err(priv->dev, "Unsupported PHY speed (%u Mbps)", mbps);
-- 
2.7.4