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Subject[PATCH v2] [RFC] rcar-vin: rcar-csi2: Correct the selection of hsfreqrange
Date
hsfreqrange should be chosen based on the calculated mbps which
is closer to the default bit rate and within the range as per
table[1]. But current calculation always selects first value which
is greater than or equal to the calculated mbps which may lead
to chosing a wrong range in some cases.

For example for 360 mbps for H3/M3N
Existing logic selects
Calculated value 360Mbps : Default 400Mbps Range [368.125 -433.125 mbps]

This hsfreqrange is out of range.

The logic is changed to get the default value which is closest to the
calculated value [1]

Calculated value 360Mbps : Default 350Mbps Range [320.625 -380.625 mpbs]

[1] specs r19uh0105ej0200-r-car-3rd-generation.pdf [Table 25.9]

There is one exectpion value 227Mbps, which may cause out of
range.

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

Signed-off-by: Suresh Udipi <sudipi@jp.adit-jv.com>
Signed-off-by: Kazuyoshi Akiyama <akiyama@nds-osk.co.jp>
---
Changes in v2:
- Added the boundary check for the maximum bit rate.

- Simplified the logic by remmoving range check
as only the closest default value covers most
of the use cases.

- Aligning the commit message based on the above change

drivers/media/platform/rcar-vin/rcar-csi2.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c b/drivers/media/platform/rcar-vin/rcar-csi2.c
index faa9fb2..6573625 100644
--- a/drivers/media/platform/rcar-vin/rcar-csi2.c
+++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
@@ -199,6 +199,7 @@ static const struct rcsi2_mbps_reg phtw_mbps_v3m_e3[] = {
/* PHY Frequency Control */
#define PHYPLL_REG 0x68
#define PHYPLL_HSFREQRANGE(n) ((n) << 16)
+#define PHYPLL_HSFREQRANGE_MAX 1500

static const struct rcsi2_mbps_reg hsfreqrange_h3_v3h_m3n[] = {
{ .mbps = 80, .reg = 0x00 },
@@ -431,16 +432,23 @@ static int rcsi2_wait_phy_start(struct rcar_csi2 *priv)
static int rcsi2_set_phypll(struct rcar_csi2 *priv, unsigned int mbps)
{
const struct rcsi2_mbps_reg *hsfreq;
+ const struct rcsi2_mbps_reg *hsfreq_prev = NULL;

- for (hsfreq = priv->info->hsfreqrange; hsfreq->mbps != 0; hsfreq++)
- if (hsfreq->mbps >= mbps)
- break;
-
- if (!hsfreq->mbps) {
+ if (mbps > PHYPLL_HSFREQRANGE_MAX) {
dev_err(priv->dev, "Unsupported PHY speed (%u Mbps)", mbps);
return -ERANGE;
}

+ for (hsfreq = priv->info->hsfreqrange; hsfreq->mbps != 0; hsfreq++) {
+ if (hsfreq->mbps >= mbps)
+ break;
+ hsfreq_prev = hsfreq;
+ }
+
+ if (hsfreq_prev &&
+ ((mbps - hsfreq_prev->mbps) <= (hsfreq->mbps - mbps)))
+ hsfreq = hsfreq_prev;
+
rcsi2_write(priv, PHYPLL_REG, PHYPLL_HSFREQRANGE(hsfreq->reg));

return 0;
--
2.7.4
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