linux-kernel - Re: [PATCH 04/10] drm/sun4i: sun6i_mipi

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Date:   Mon, 5 Nov 2018 11:44:36 +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
Subject: Re: [PATCH 04/10] drm/sun4i: sun6i_mipi_dsi: Setup burst mode

On Sat, Nov 03, 2018 at 03:38:54PM +0530, Jagan Teki wrote:
> Setting up burst mode display would require to compute
> - Horizontal timing edge values to fill burst drq register
> - Line, sync values to fill burst line register
> 
> Since there is no direct documentation for these computations
> the edge and line formulas are taken from BSP code
> (in drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
> line_num = panel->lcd_ht*dsi_pixel_bits[panel->lcd_dsi_format]/
> 	  (8*panel->lcd_dsi_lane);
> edge1 = sync_point+(panel->lcd_x+panel->lcd_hbp+20)*
> 	dsi_pixel_bits[panel->lcd_dsi_format] /(8*panel->lcd_dsi_lane);
> edge1 = (edge1>line_num)?line_num:edge1;
> edge0 = edge1+(panel->lcd_x+40)*tcon_div/8;
> edge0 = (edge0>line_num)?(edge0-line_num):1;
> 
> Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> ---
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 48 +++++++++++++++++++++-----
>  1 file changed, 40 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index 4965b2c71e4c..b6c01891df36 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -375,20 +375,52 @@ static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
>  				  struct drm_display_mode *mode)
>  {
>  	struct mipi_dsi_device *device = dsi->device;
> +	unsigned int Bpp = mipi_dsi_pixel_format_to_bpp(device->format);
> +	u32 line_num, edge0, edge1, hact_sync_bp;
> +	u32 sync_point, tcon_div;
>  	u32 val = 0;
>  
> -	if ((mode->hsync_start - mode->hdisplay) > 20) {
> -		/* Maaaaaagic */
> -		u16 drq = (mode->hsync_start - mode->hdisplay) - 20;
> +	if (device->mode_flags != MIPI_DSI_MODE_VIDEO_BURST) {
> +		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;
> +			drq *= Bpp;
> +			drq /= 32;
>  
> -		val = (SUN6I_DSI_TCON_DRQ_ENABLE_MODE |
> -		       SUN6I_DSI_TCON_DRQ_SET(drq));
> +			val = (SUN6I_DSI_TCON_DRQ_ENABLE_MODE |
> +			       SUN6I_DSI_TCON_DRQ_SET(drq));
> +		}
> +
> +		regmap_write(dsi->regs, SUN6I_DSI_TCON_DRQ_REG, val);
> +
> +		return;
>  	}

Having functions to compute drq, the line_number and so on would help
the readibility a lot.

> -	regmap_write(dsi->regs, SUN6I_DSI_TCON_DRQ_REG, val);
> +	sync_point = 40;
> +	tcon_div = 8;	/* FIXME need to retrive the divider from TCON */

Then do it. Especially since you have exactly 0 guarantee of the
divider being 8.

(also, s/retrive/retrieve/)

> +
> +	line_num = mode->htotal * Bpp / (8 * device->lanes);
> +	/* Horizental timings duration excluding front porch */

Horizontal

Maxime

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

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