linux-kernel - [PATCH v1 2/9] drm/bridge: tc358768: fix PLL parameters computation

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Message-Id: <20230427142934.55435-3-francesco@dolcini.it>
Date:   Thu, 27 Apr 2023 16:29:27 +0200
From:   Francesco Dolcini <francesco@...cini.it>
To:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        tomi.valkeinen@...asonboard.com, dri-devel@...ts.freedesktop.org
Cc:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: [PATCH v1 2/9] drm/bridge: tc358768: fix PLL parameters computation

From: Francesco Dolcini <francesco.dolcini@...adex.com>

According to Toshiba documentation the PLL input clock after the divider
should be not less than 4MHz, fix the PLL parameters computation
accordingly.

Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
---
 drivers/gpu/drm/bridge/tc358768.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
index 8f349bf4fc32..e9e3f9e02bba 100644
--- a/drivers/gpu/drm/bridge/tc358768.c
+++ b/drivers/gpu/drm/bridge/tc358768.c
@@ -334,13 +334,17 @@ static int tc358768_calc_pll(struct tc358768_priv *priv,
 		u32 fbd;
 
 		for (fbd = 0; fbd < 512; ++fbd) {
-			u32 pll, diff;
+			u32 pll, diff, pll_in;
 
 			pll = (u32)div_u64((u64)refclk * (fbd + 1), divisor);
 
 			if (pll >= max_pll || pll < min_pll)
 				continue;
 
+			pll_in = (u32)div_u64((u64)refclk, prd + 1);
+			if (pll_in < 4000000)
+				continue;
+
 			diff = max(pll, target_pll) - min(pll, target_pll);
 
 			if (diff < best_diff) {
-- 
2.25.1