linux-kernel - Re: [PATCH v2 04/12] drm/sun4i: sun6i_mipi_dsi: Simplify drq set to support all modes

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Date:   Mon, 19 Nov 2018 09:32:43 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Michael Trimarchi <michael@...rulasolutions.com>,
        TL Lim <tllim@...e64.org>, linux-sunxi@...glegroups.com,
        linux-amarula@...rulasolutions.com
Subject: Re: [PATCH v2 04/12] drm/sun4i: sun6i_mipi_dsi: Simplify drq set to
 support all modes

On Fri, Nov 16, 2018 at 10:09:08PM +0530, Jagan Teki wrote:
> Allwinner MIPI DSI DRQ set value can be varied with respective
> video modes.
> - burst mode the set value is always 0
> - video modes whose front porch greater than 20, the set value
>   can be computed based front porch and bpp.
> - video modes whose front porch is not greater than 20, the set value
>   is simply 0
> 
> This patch simplifies existing drq set value code by grouping
> into sun6i_dsi_get_drq and support all video modes.
> 
> Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> ---
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 38 ++++++++++++++++----------
>  1 file changed, 23 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index efd08bfd0cb8..d60955880c43 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -363,6 +363,26 @@ static void sun6i_dsi_inst_init(struct sun6i_dsi *dsi,
>  		     SUN6I_DSI_INST_JUMP_CFG_NUM(1));
>  };
>  
> +static int sun6i_dsi_get_drq(struct sun6i_dsi *dsi,
> +			      struct drm_display_mode *mode)
> +{
> +	struct mipi_dsi_device *device = dsi->device;
> +	int drq = 0;

So, here, you declaring a variable called drq, set to 0.

> +	if (device->mode_flags & MIPI_DSI_MODE_VIDEO_BURST)
> +		return drq;

That you return here. You could just return 0, to be clearer.

> +	if ((mode->hsync_start - mode->hdisplay) > 20) {
> +		/* Maaaaaagic */
> +		u16 drq = (mode->hsync_start - mode->hdisplay) - 20;

You re-declare a variable with the same name here, but a different
type....

> +		drq *= mipi_dsi_pixel_format_to_bpp(device->format);
> +		drq /= 32;
> +	}
> +
> +	return drq;

And then return the first one? How is that even working?

> +
>  static u16 sun6i_dsi_get_timings_vblk(struct sun6i_dsi *dsi,
>  				      struct drm_display_mode *mode, u16 hblk)
>  {
> @@ -478,21 +498,9 @@ static u16 sun6i_dsi_get_video_start_delay(struct sun6i_dsi *dsi,
>  static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
>  				  struct drm_display_mode *mode)
>  {
> -	struct mipi_dsi_device *device = dsi->device;
> -	u32 val = 0;
> -
> -	if ((mode->hsync_start - mode->hdisplay) > 20) {
> -		/* Maaaaaagic */
> -		u16 drq = (mode->hsync_start - mode->hdisplay) - 20;
> -
> -		drq *= mipi_dsi_pixel_format_to_bpp(device->format);
> -		drq /= 32;
> -
> -		val = (SUN6I_DSI_TCON_DRQ_ENABLE_MODE |
> -		       SUN6I_DSI_TCON_DRQ_SET(drq));
> -	}
> -
> -	regmap_write(dsi->regs, SUN6I_DSI_TCON_DRQ_REG, val);
> +	regmap_write(dsi->regs, SUN6I_DSI_TCON_DRQ_REG,
> +		     SUN6I_DSI_TCON_DRQ_ENABLE_MODE |
> +		     SUN6I_DSI_TCON_DRQ_SET(sun6i_dsi_get_drq(dsi, mode)));

On top of that, you now enable the DRQ stuff all the time, while it
was conditional before.

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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