linux-kernel - Re: [PATCH v5 04/10] drm: bridge: samsung-dsim: complete the CLKLANE

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Date:   Thu, 7 Dec 2023 17:58:25 +0100
From:   Frieder Schrempf <frieder.schrempf@...tron.de>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>,
        linux-kernel@...r.kernel.org
Cc:     Maxime Ripard <mripard@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jonas Karlman <jonas@...boo.se>,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        dri-devel@...ts.freedesktop.org,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        michael@...rulasolutions.com,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v5 04/10] drm: bridge: samsung-dsim: complete the
 CLKLANE_STOP setting

On 07.12.23 15:16, Dario Binacchi wrote:
> The patch completes the setting of CLKLANE_STOP for the imx8mn and imx8mp
> platforms (i. e. not exynos).

This also affects i.MX8MM, so better just mention i.MX in general in the
commit message.

> 
> Co-developed-by: Michael Trimarchi <michael@...rulasolutions.com>
> Signed-off-by: Michael Trimarchi <michael@...rulasolutions.com>
> Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> ---
> 
> (no changes since v1)
> 
>  drivers/gpu/drm/bridge/samsung-dsim.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 15bf05b2bbe4..13f181c99d7e 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -96,6 +96,7 @@
>  #define DSIM_MFLUSH_VS			BIT(29)
>  /* This flag is valid only for exynos3250/3472/5260/5430 */
>  #define DSIM_CLKLANE_STOP		BIT(30)
> +#define DSIM_NON_CONTINUOUS_CLKLANE	BIT(31)
>  
>  /* DSIM_ESCMODE */
>  #define DSIM_TX_TRIGGER_RST		BIT(4)
> @@ -945,8 +946,12 @@ static int samsung_dsim_init_link(struct samsung_dsim *dsi)
>  	 * power consumption.
>  	 */
>  	if (driver_data->has_clklane_stop &&
> -	    dsi->mode_flags & MIPI_DSI_CLOCK_NON_CONTINUOUS)
> +	    dsi->mode_flags & MIPI_DSI_CLOCK_NON_CONTINUOUS) {
> +		if (!samsung_dsim_hw_is_exynos(dsi->plat_data->hw_type))
> +			reg |= DSIM_NON_CONTINUOUS_CLKLANE;
> +
>  		reg |= DSIM_CLKLANE_STOP;
> +	}

I really wonder what the difference between DSIM_NON_CONTINUOUS_CLKLANE
and DSIM_CLKLANE_STOP is.

If Exynos only has the latter, it's pretty clear what to use. But as
i.MX has both of these bits, should both be set? Or is setting
DSIM_NON_CONTINUOUS_CLKLANE enough and we should leave DSIM_CLKLANE_STOP
alone?

Maybe someone has a clue here. The description of the bits in the RM is:

DSIM_NON_CONTINUOUS_CLKLANE - Non-continuous clock mode
DSIM_CLKLANE_STOP -  PHY clock lane On/Off for ESD

>  	samsung_dsim_write(dsi, DSIM_CONFIG_REG, reg);
>  
>  	lanes_mask = BIT(dsi->lanes) - 1;