linux-kernel - [PATCH V3 1/2] drm/bridge: samsung-dsim: Set P divider based on min/max of fin pll

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Date: Sat,  1 Jun 2024 09:41:01 -0500
From: Adam Ford <aford173@...il.com>
To: dri-devel@...ts.freedesktop.org
Cc: aford@...conembedded.com,
	Adam Ford <aford173@...il.com>,
	Frieder Schrempf <frieder.schrempf@...tron.de>,
	Marek Vasut <marex@...x.de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Inki Dae <inki.dae@...sung.com>,
	Jagan Teki <jagan@...rulasolutions.com>,
	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>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Marco Felsch <m.felsch@...gutronix.de>,
	Michael Tretter <m.tretter@...gutronix.de>,
	linux-kernel@...r.kernel.org
Subject: [PATCH V3 1/2] drm/bridge: samsung-dsim: Set P divider based on min/max of fin pll

The P divider should be set based on the min and max values of
the fin pll which may vary between different platforms.
These ranges are defined per platform, but hard-coded values
were used instead which resulted in a smaller range available
on the i.MX8M[MNP] than what was possible.

As noted by Frieder, there are descripencies between the reference
manuals of the Mini, Nano and Plus, so I reached out to my NXP
rep and got the following response regarding the varing notes
in the documentation.

"Yes it is definitely wrong, the one that is part of the NOTE in
MIPI_DPHY_M_PLLPMS register table against PMS_P, PMS_M and PMS_S is
not correct. I will report this to Doc team, the one customer should
be take into account is the Table 13-40 DPHY PLL Parameters and the
Note above."

With this patch, the clock rates now match the values used in NXP's
downstream kernel.

Fixes: 846307185f0f ("drm/bridge: samsung-dsim: update PLL reference clock")
Signed-off-by: Adam Ford <aford173@...il.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@...tron.de>
Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de>
Reviewed-by: Marek Vasut <marex@...x.de>
Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

---
V2:  Only update the commit message to reflect why these values
     were chosen.  No code change present

V3:  No Changes

diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
index 95fedc68b0ae..8476650c477c 100644
--- a/drivers/gpu/drm/bridge/samsung-dsim.c
+++ b/drivers/gpu/drm/bridge/samsung-dsim.c
@@ -574,8 +574,8 @@ static unsigned long samsung_dsim_pll_find_pms(struct samsung_dsim *dsi,
 	u16 _m, best_m;
 	u8 _s, best_s;
 
-	p_min = DIV_ROUND_UP(fin, (12 * MHZ));
-	p_max = fin / (6 * MHZ);
+	p_min = DIV_ROUND_UP(fin, (driver_data->pll_fin_max * MHZ));
+	p_max = fin / (driver_data->pll_fin_min * MHZ);
 
 	for (_p = p_min; _p <= p_max; ++_p) {
 		for (_s = 0; _s <= 5; ++_s) {
-- 
2.43.0