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

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Message-ID: <20170315165511.336783bb.john@metanate.com>
Date:   Wed, 15 Mar 2017 16:55:11 +0000
From:   John Keeping <john@...anate.com>
To:     Brian Norris <briannorris@...omium.org>,
        Chris Zhong <zyw@...k-chips.com>
Cc:     Heiko Stuebner <heiko@...ech.de>, David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.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

On Wed, 15 Mar 2017 09:47:29 -0700, Brian Norris wrote:

> 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.

If RK3399 is broken without grf_clk, I wonder if there should be a flag
in dw_mipi_dsi_plat_data so that the driver can enforce "required for
RK3399".


John