linux-kernel - Re: [PATCH 2/3] drm/rockchip/dsi: enable the grf clk before writing grf registers

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Message-ID: <20170315164726.GA54312@google.com>
Date:   Wed, 15 Mar 2017 09:47:29 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Chris Zhong <zyw@...k-chips.com>
Cc:     linux-rockchip@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        Mark Yao <mark.yao@...k-chips.com>
Subject: Re: [PATCH 2/3] drm/rockchip/dsi: enable the grf clk before writing
 grf registers

Hi Chris,

On Wed, Mar 15, 2017 at 04:42:31PM +0800, Chris Zhong wrote:
> For RK3399, the grf clk should be enabled before writing grf registers,
> otherwise the register value can not be changed.
> 
> Signed-off-by: Chris Zhong <zyw@...k-chips.com>
> ---
> 
>  drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> index f84f9ae..d8f24f2 100644
> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> @@ -291,6 +291,7 @@ struct dw_mipi_dsi {
>  	struct regmap *grf_regmap;
>  	void __iomem *base;
>  
> +	struct clk *grf_clk;
>  	struct clk *pllref_clk;
>  	struct clk *pclk;
>  	struct clk *phy_cfg_clk;
> @@ -979,6 +980,16 @@ static void dw_mipi_dsi_encoder_enable(struct drm_encoder *encoder)
>  	dw_mipi_dsi_dphy_interface_config(dsi);
>  	dw_mipi_dsi_clear_err(dsi);
>  
> +	/*
> +	 * For the RK3399, the clk of grf must be enabled before writing grf
> +	 * register.
> +	 */
> +	ret = clk_prepare_enable(dsi->grf_clk);
> +	if (ret) {
> +		dev_err(dsi->dev, "Failed to enable grf_clk\n");
> +		return;
> +	}
> +
>  	if (pdata->grf_dsi0_mode_reg)
>  		regmap_write(dsi->grf_regmap, pdata->grf_dsi0_mode_reg,
>  			     pdata->grf_dsi0_mode);
> @@ -1003,6 +1014,8 @@ static void dw_mipi_dsi_encoder_enable(struct drm_encoder *encoder)
>  	regmap_write(dsi->grf_regmap, pdata->grf_switch_reg, val);
>  	dev_dbg(dsi->dev, "vop %s output to dsi0\n", (mux) ? "LIT" : "BIG");
>  	dsi->dpms_mode = DRM_MODE_DPMS_ON;
> +
> +	clk_disable_unprepare(dsi->grf_clk);
>  }
>  
>  static int
> @@ -1238,6 +1251,17 @@ static int dw_mipi_dsi_bind(struct device *dev, struct device *master,
>  		dev_dbg(dev, "have not phy_cfg_clk\n");
>  	}
>  
> +	dsi->grf_clk = devm_clk_get(dev, "grf");
> +	if (IS_ERR(dsi->grf_clk)) {
> +		ret = PTR_ERR(dsi->grf_clk);
> +		if (ret != -ENOENT) {
> +			dev_err(dev, "Unable to get grf_clk: %d\n", ret);

If you're going to print an error, you should probably check for
-EPROBE_DEFER. This driver isn't quite consistent about this.

> +			return ret;
> +		}
> +		dsi->grf_clk = NULL;
> +		dev_dbg(dev, "have not grf_clk\n");

The wording is a little awkward; maybe "no grf_clk provided\n"?

Also, to be clear, this clock is required for RK3399, but not for others
(e.g., RK3288) right? I guess this makes sense then, to just treat it as
optional for all cases, even if you document it as "required" for
RK3399.

Brian

> +	}
> +
>  	ret = clk_prepare_enable(dsi->pllref_clk);
>  	if (ret) {
>  		dev_err(dev, "%s: Failed to enable pllref_clk\n", __func__);

Brian