linux-kernel - Re: [PATCH] drm/bridge/synopsys: dsi: add optional pixel clock

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Date:   Fri, 27 Oct 2017 10:06:35 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Philippe Cornu <philippe.cornu@...com>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Bhumika Goyal <bhumirks@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     Yannick Fertre <yannick.fertre@...com>,
        Vincent Abriou <vincent.abriou@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Gabriel Fernandez <gabriel.fernandez@...com>,
        Ludovic Barre <ludovic.barre@...com>,
        Fabien Dessenne <fabien.dessenne@...com>,
        Mickael Reulier <mickael.reulier@...com>
Subject: Re: [PATCH] drm/bridge/synopsys: dsi: add optional pixel clock

Hi Philippe,

On Thu, 2017-10-26 at 18:09 +0200, Philippe Cornu wrote:
> The pixel clock is optional. When available, it offers a better
> preciseness for timing computations.
> 
> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> index d9cca4f..8b3787d 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> @@ -225,6 +225,7 @@ struct dw_mipi_dsi {
>  	void __iomem *base;
>  
>  	struct clk *pclk;
> +	struct clk *px_clk;
>  
>  	unsigned int lane_mbps; /* per lane */
>  	u32 channel;
> @@ -753,24 +754,28 @@ void dw_mipi_dsi_bridge_mode_set(struct drm_bridge *bridge,
>  	struct dw_mipi_dsi *dsi = bridge_to_dsi(bridge);
>  	const struct dw_mipi_dsi_phy_ops *phy_ops = dsi->plat_data->phy_ops;
>  	void *priv_data = dsi->plat_data->priv_data;
> +	struct drm_display_mode px_clk_mode = *mode;
>  	int ret;
>  
>  	clk_prepare_enable(dsi->pclk);
>  
> -	ret = phy_ops->get_lane_mbps(priv_data, mode, dsi->mode_flags,
> +	if (dsi->px_clk)
> +		px_clk_mode.clock = clk_get_rate(dsi->px_clk) / 1000;

I don't understand why is the pixel clock rate divided by 1000 different
from the mode clock in the first place? If px_clk is just the DPI input
pixel clock signal from the display controller, I'd expect the mode to
be adjusted correctly.

> +
> +	ret = phy_ops->get_lane_mbps(priv_data, &px_clk_mode, dsi->mode_flags,
>  				     dsi->lanes, dsi->format, &dsi->lane_mbps);
>  	if (ret)
>  		DRM_DEBUG_DRIVER("Phy get_lane_mbps() failed\n");
>  
>  	pm_runtime_get_sync(dsi->dev);
>  	dw_mipi_dsi_init(dsi);
> -	dw_mipi_dsi_dpi_config(dsi, mode);
> +	dw_mipi_dsi_dpi_config(dsi, &px_clk_mode);
>  	dw_mipi_dsi_packet_handler_config(dsi);
>  	dw_mipi_dsi_video_mode_config(dsi);
> -	dw_mipi_dsi_video_packet_config(dsi, mode);
> +	dw_mipi_dsi_video_packet_config(dsi, &px_clk_mode);
>  	dw_mipi_dsi_command_mode_config(dsi);
> -	dw_mipi_dsi_line_timer_config(dsi, mode);
> -	dw_mipi_dsi_vertical_timing_config(dsi, mode);
> +	dw_mipi_dsi_line_timer_config(dsi, &px_clk_mode);
> +	dw_mipi_dsi_vertical_timing_config(dsi, &px_clk_mode);
>  
>  	dw_mipi_dsi_dphy_init(dsi);
>  	dw_mipi_dsi_dphy_timing_config(dsi);
> @@ -784,7 +789,7 @@ void dw_mipi_dsi_bridge_mode_set(struct drm_bridge *bridge,
>  
>  	dw_mipi_dsi_dphy_enable(dsi);
>  
> -	dw_mipi_dsi_wait_for_two_frames(mode);
> +	dw_mipi_dsi_wait_for_two_frames(&px_clk_mode);
>  
>  	/* Switch to cmd mode for panel-bridge pre_enable & panel prepare */
>  	dw_mipi_dsi_set_mode(dsi, 0);
> @@ -878,6 +883,13 @@ static int dw_mipi_dsi_bridge_attach(struct drm_bridge *bridge)
>  		return ERR_PTR(ret);
>  	}
>  
> +	dsi->px_clk = devm_clk_get(dev, "px_clk");

Is "px_clk" what the pixel clock is called in the datasheet?

If this is probed from DT, the new optional property must be documented
in the binding docs.

> +	if (IS_ERR(dsi->px_clk)) {
> +		ret = PTR_ERR(dsi->px_clk);

Better leave ret == 0 for -ENOENT, but return the error for all others.

> +		dev_dbg(dev, "Unable to get optional px_clk: %d\n", ret);
> +		dsi->px_clk = NULL;
> +	}
> +
>  	/*
>  	 * Note that the reset was not defined in the initial device tree, so
>  	 * we have to be prepared for it not being found.

regards
Philipp