[PATCH 16/26] phy: dphy: Correct clk_pre parameter

[Dario Binacchi]

From: Michael Trimarchi <michael at amarulasolutions.com>

Upstream linux commit 9a8406ba1a9a29.

The D-PHY specification (v1.2) explicitly mentions that the T-CLK-PRE
parameter's unit is Unit Interval(UI) and the minimum value is 8.  Also,
kernel doc of the 'clk_pre' member of struct phy_configure_opts_mipi_dphy
mentions that it should be in UI.  However, the dphy core driver wrongly
sets 'clk_pre' to 8000, which seems to hint that it's in picoseconds.

So, let's fix the dphy core driver to correctly reflect the T-CLK-PRE
parameter's minimum value according to the D-PHY specification.

I'm assuming that all impacted custom drivers shall program values in
TxByteClkHS cycles into hardware for the T-CLK-PRE parameter.  The D-PHY
specification mentions that the frequency of TxByteClkHS is exactly 1/8
the High-Speed(HS) bit rate(each HS bit consumes one UI).  So, relevant
custom driver code is changed to program those values as
DIV_ROUND_UP(cfg->clk_pre, BITS_PER_BYTE), then.

Note that I've only tested the patch with RM67191 DSI panel on i.MX8mq EVK.
Help is needed to test with other i.MX8mq, Meson and Rockchip platforms,
as I don't have the hardwares.

Tested-by: Liu Ying <victor.liu at nxp.com> # RM67191 DSI panel on i.MX8mq EVK
Reviewed-by: Andrzej Hajda <andrzej.hajda at intel.com>
Reviewed-by: Neil Armstrong <narmstrong at baylibre.com> # for phy-meson-axg-mipi-dphy.c
Tested-by: Neil Armstrong <narmstrong at baylibre.com> # for phy-meson-axg-mipi-dphy.c
Tested-by: Guido Günther <agx at sigxcpu.org> # Librem 5 (imx8mq) with it's rather picky panel
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Signed-off-by: Liu Ying <victor.liu at nxp.com>
Link: https://lore.kernel.org/r/20220124024007.1465018-1-victor.liu@nxp.com
Signed-off-by: Vinod Koul <vkoul at kernel.org>
Signed-off-by: Michael Trimarchi <michael at amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi at amarulasolutions.com>
---

 drivers/phy/meson-axg-mipi-dphy.c | 2 +-
 drivers/phy/phy-core-mipi-dphy.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/phy/meson-axg-mipi-dphy.c b/drivers/phy/meson-axg-mipi-dphy.c
index 3f89de19970b..fb10ccca6ac1 100644
--- a/drivers/phy/meson-axg-mipi-dphy.c
+++ b/drivers/phy/meson-axg-mipi-dphy.c
@@ -237,7 +237,7 @@ static int phy_meson_axg_mipi_dphy_power_on(struct phy *phy)
 		     (DIV_ROUND_UP(priv->config.clk_zero, temp) << 16) |
 		     (DIV_ROUND_UP(priv->config.clk_prepare, temp) << 24));
 	regmap_write(priv->regmap, MIPI_DSI_CLK_TIM1,
-		     DIV_ROUND_UP(priv->config.clk_pre, temp));
+		     DIV_ROUND_UP(priv->config.clk_pre, BITS_PER_BYTE));
 
 	regmap_write(priv->regmap, MIPI_DSI_HS_TIM,
 		     DIV_ROUND_UP(priv->config.hs_exit, temp) |
diff --git a/drivers/phy/phy-core-mipi-dphy.c b/drivers/phy/phy-core-mipi-dphy.c
index 79cab9125002..27cff85709d9 100644
--- a/drivers/phy/phy-core-mipi-dphy.c
+++ b/drivers/phy/phy-core-mipi-dphy.c
@@ -36,7 +36,7 @@ static int phy_mipi_dphy_calc_config(unsigned long pixel_clock,
 
 	cfg->clk_miss = 0;
 	cfg->clk_post = 60000 + 52 * ui;
-	cfg->clk_pre = 8000;
+	cfg->clk_pre = 8;
 	cfg->clk_prepare = 38000;
 	cfg->clk_settle = 95000;
 	cfg->clk_term_en = 0;
-- 
2.43.0