[PATCH v2] phy: dphy: Correct clk_pre parameter

[Liu Ying]

Hi Heiko, Wyon,

On Wed, 2022-01-19 at 10:37 +0800, Liu Ying wrote:
> 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.
> And, the kernel doc of the 'clk_pre' member wrongly says the minimum value
> is '8 UI', instead of 8.
> 
> So, let's fix both the dphy core driver and the kernel doc of the 'clk_pre'
> member to correctly reflect the T-CLK-PRE parameter's unit and the 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.
> 
> Fixes: 2ed869990e14 ("phy: Add MIPI D-PHY configuration options")
> Cc: Andrzej Hajda <andrzej.hajda at intel.com>
> Cc: Neil Armstrong <narmstrong at baylibre.com>
> Cc: Robert Foss <robert.foss at linaro.org>
> Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
> Cc: Jonas Karlman <jonas at kwiboo.se>
> Cc: Jernej Skrabec <jernej.skrabec at gmail.com>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Kishon Vijay Abraham I <kishon at ti.com>
> Cc: Vinod Koul <vkoul at kernel.org>
> Cc: Kevin Hilman <khilman at baylibre.com>
> Cc: Jerome Brunet <jbrunet at baylibre.com>
> Cc: Martin Blumenstingl <martin.blumenstingl at googlemail.com>
> Cc: Heiko Stuebner <heiko at sntech.de>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Guido Günther <agx at sigxcpu.org>
> Tested-by: Liu Ying <victor.liu at nxp.com> # RM67191 DSI panel on i.MX8mq EVK
> Signed-off-by: Liu Ying <victor.liu at nxp.com>
> ---
> v1->v2:
> * Use BITS_PER_BYTE macro. (Andrzej)
> * Drop dsi argument from ui2bc() in nwl-dsi.c.
> 
>  drivers/gpu/drm/bridge/nwl-dsi.c                 | 12 +++++-------
>  drivers/phy/amlogic/phy-meson-axg-mipi-dphy.c    |  3 ++-
>  drivers/phy/phy-core-mipi-dphy.c                 |  4 ++--
>  drivers/phy/rockchip/phy-rockchip-inno-dsidphy.c |  3 ++-
>  include/linux/phy/phy-mipi-dphy.h                |  2 +-
>  5 files changed, 12 insertions(+), 12 deletions(-)

[...]

> diff --git a/drivers/phy/phy-core-mipi-dphy.c b/drivers/phy/phy-core-mipi-dphy.c
> index 288c9c67aa74..ccb4045685cd 100644
> --- a/drivers/phy/phy-core-mipi-dphy.c
> +++ b/drivers/phy/phy-core-mipi-dphy.c
> @@ -36,7 +36,7 @@ int phy_mipi_dphy_get_default_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;
> @@ -97,7 +97,7 @@ int phy_mipi_dphy_config_validate(struct phy_configure_opts_mipi_dphy *cfg)
>  	if (cfg->clk_post < (60000 + 52 * ui))
>  		return -EINVAL;
>  
> -	if (cfg->clk_pre < 8000)
> +	if (cfg->clk_pre < 8)
>  		return -EINVAL;
>  
>  	if (cfg->clk_prepare < 38000 || cfg->clk_prepare > 95000)
> diff --git a/drivers/phy/rockchip/phy-rockchip-inno-dsidphy.c b/drivers/phy/rockchip/phy-rockchip-inno-dsidphy.c
> index 347dc79a18c1..630e01b5c19b 100644
> --- a/drivers/phy/rockchip/phy-rockchip-inno-dsidphy.c
> +++ b/drivers/phy/rockchip/phy-rockchip-inno-dsidphy.c
> @@ -5,6 +5,7 @@
>   * Author: Wyon Bi <bivvy.bi at rock-chips.com>
>   */
>  
> +#include <linux/bits.h>
>  #include <linux/kernel.h>
>  #include <linux/clk.h>
>  #include <linux/iopoll.h>
> @@ -364,7 +365,7 @@ static void inno_dsidphy_mipi_mode_enable(struct inno_dsidphy *inno)
>  	 * The value of counter for HS Tclk-pre
>  	 * Tclk-pre = Tpin_txbyteclkhs * value
>  	 */
> -	clk_pre = DIV_ROUND_UP(cfg->clk_pre, t_txbyteclkhs);
> +	clk_pre = DIV_ROUND_UP(cfg->clk_pre, BITS_PER_BYTE);

For the Rockchip part, can you please give a test? Any comments?

We already have T-b tags on i.MX8mq and Meson platforms.

Regards,
Liu Ying

>  
>  	/*
>  	 * The value of counter for HS Tlpx Time
> diff --git a/include/linux/phy/phy-mipi-dphy.h b/include/linux/phy/phy-mipi-dphy.h
> index a877ffee845d..59a5e77ab409 100644
> --- a/include/linux/phy/phy-mipi-dphy.h
> +++ b/include/linux/phy/phy-mipi-dphy.h
> @@ -42,7 +42,7 @@ struct phy_configure_opts_mipi_dphy {
>  	 * the transmitter prior to any associated Data Lane beginning
>  	 * the transition from LP to HS mode.
>  	 *
> -	 * Minimum value: 8 UI
> +	 * Minimum value: 8
>  	 */
>  	unsigned int		clk_pre;
>