linux-kernel - Re: [PATCH v2] drm/bridge/synopsys: dsi: add optional pixel clock

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Date:   Mon, 15 Jan 2018 14:52:08 +0100
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Philippe Cornu <philippe.cornu@...com>,
        Archit Taneja <architt@...eaurora.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        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>,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH v2] drm/bridge/synopsys: dsi: add optional pixel clock

On 12.01.2018 17:25, Philippe Cornu wrote:
> The pixel clock is optional. When available, it offers a better
> preciseness for timing computations and allows to reduce the extra dsi
> bandwidth in burst mode (from ~20% to ~10-12%, hw platform dependent).
>
> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
> ---
> Changes in v2: Improve px_clk probing in case of ENOENT dt returned value
> (thanks to Philipp Zabel & Andrzej Hajda comments)
>
>  drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 26 ++++++++++++++++++++------
>  1 file changed, 20 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 c39c7dce20ed..62fcff881b98 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;
> +
> +	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 +883,15 @@ __dw_mipi_dsi_probe(struct platform_device *pdev,
>  		return ERR_PTR(ret);
>  	}
>  
> +	dsi->px_clk = devm_clk_get(dev, "px_clk");
> +	if (PTR_ERR(dsi->px_clk) == -ENOENT) {
> +		dsi->px_clk = NULL;
> +	} else if (IS_ERR(dsi->px_clk)) {
> +		ret = PTR_ERR(dsi->px_clk);
> +		dev_err(dev, "Unable to get optional px_clk: %d\n", ret);
> +		dsi->px_clk = NULL;
> +	}
> +
As I understand on fail you just log an error and continue?
The code could be slightly simplified, for example:
dsi->px_clk = devm_clk_get(dev, "px_clk");
if (IS_ERR(dsi->px_clk)) {
        ret = PTR_ERR(dsi->px_clk);
        if (ret != ENOENT)
                dev_err(dev, "Unable to get optional px_clk: %d\n", ret);
        dsi->px_clk = NULL;
}

With or without this change:

Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>

 --
Regards
Andrzej


>  	/*
>  	 * Note that the reset was not defined in the initial device tree, so
>  	 * we have to be prepared for it not being found.