linux-kernel - [PATCH 5.17 0732/1126] phy: dphy: Correct lpx parameter and its derivatives(ta

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Date:   Tue,  5 Apr 2022 09:24:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Maxime Ripard <mripard@...nel.org>,
        Guido Günther <agx@...xcpu.org>,
        Liu Ying <victor.liu@....com>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.17 0732/1126] phy: dphy: Correct lpx parameter and its derivatives(ta_{get,go,sure})

From: Liu Ying <victor.liu@....com>

[ Upstream commit 3153fa38e38af566cf6454a03b1dbadaf6f323c0 ]

According to the comment of the function phy_mipi_dphy_get_default_config(),
it uses minimum D-PHY timings based on MIPI D-PHY specification.  They are
derived from the valid ranges specified in Section 6.9, Table 14, Page 41
of the D-PHY specification (v1.2).  The table 14 explicitly mentions that
the minimum T-LPX parameter is 50 nanoseconds and the minimum TA-SURE
parameter is T-LPX nanoseconds.  Likewise, the kernel doc of the 'lpx' and
'ta_sure' members of struct phy_configure_opts_mipi_dphy mentions that
the minimum values are 50000 picoseconds and @lpx picoseconds respectively.
Also, the function phy_mipi_dphy_config_validate() checks if cfg->lpx is
less than 50000 picoseconds and if cfg->ta_sure is less than cfg->lpx,
which hints the same minimum values.

Without this patch, the function phy_mipi_dphy_get_default_config()
wrongly sets cfg->lpx to 60000 picoseconds and cfg->ta_sure to 2 * cfg->lpx.
So, let's correct them to 50000 picoseconds and cfg->lpx respectively.

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.

Fixes: dddc97e82303 ("phy: dphy: Add configuration helpers")
Cc: Andrzej Hajda <andrzej.hajda@...el.com>
Cc: Neil Armstrong <narmstrong@...libre.com>
Cc: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Cc: Kishon Vijay Abraham I <kishon@...com>
Cc: Vinod Koul <vkoul@...nel.org>
Cc: Heiko Stuebner <heiko@...ech.de>
Cc: Maxime Ripard <mripard@...nel.org>
Cc: Guido Günther <agx@...xcpu.org>
Signed-off-by: Liu Ying <victor.liu@....com>
Link: https://lore.kernel.org/r/20220216071257.1647703-1-victor.liu@nxp.com
Signed-off-by: Vinod Koul <vkoul@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/phy/phy-core-mipi-dphy.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/phy/phy-core-mipi-dphy.c b/drivers/phy/phy-core-mipi-dphy.c
index ccb4045685cd..929e86d6558e 100644
--- a/drivers/phy/phy-core-mipi-dphy.c
+++ b/drivers/phy/phy-core-mipi-dphy.c
@@ -64,10 +64,10 @@ int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
 	cfg->hs_trail = max(4 * 8 * ui, 60000 + 4 * 4 * ui);

 	cfg->init = 100;
-	cfg->lpx = 60000;
+	cfg->lpx = 50000;
 	cfg->ta_get = 5 * cfg->lpx;
 	cfg->ta_go = 4 * cfg->lpx;
-	cfg->ta_sure = 2 * cfg->lpx;
+	cfg->ta_sure = cfg->lpx;
 	cfg->wakeup = 1000;

 	cfg->hs_clk_rate = hs_clk_rate;
-- 
2.34.1