linux-kernel - Re: [PATCH v9 3/5] drm/sun4i: sun6i_mipi_dsi: Support vblk timing for 4-lane devices

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Date:   Mon, 4 Mar 2019 16:49:11 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Chen-Yu Tsai <wens@...e.org>, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-amarula@...rulasolutions.com,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH v9 3/5] drm/sun4i: sun6i_mipi_dsi: Support vblk timing
 for 4-lane devices

On Sun, Mar 03, 2019 at 11:05:25PM +0530, Jagan Teki wrote:
> Like other dsi setup timings, or hblk for that matter vblk would
> also require compute the timings based payload equation along with
> packet overhead.
> 
> But, on the other hand vblk computation is also depends on device
> lane number.
> - for 4 lane devices, it is computed based on vtotal, packet overhead
>   along with hblk value.
> - for others devices, it is simply 0
> 
> BSP code from BPI-M64-bsp is computing vblk as for 4-lane devices
> (from linux-sunxi
> drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
> 
> tmp = (ht*dsi_pixel_bits[format]/8)*vt-(4+dsi_hblk+2);
> dsi_vblk = (lane-tmp%lane);
> 
> So, update the vblk timing calculation to support all type of
> devices.
> 
> Tested on 2-lane, 4-lane MIPI-DSI LCD panels.

You should be explaining which issue you faced, in which setup, what
were its symptoms and how that solution is fixing it.

> Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> Tested-by: Merlijn Wajer <merlijn@...zup.org>
> ---
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 27 +++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index 140e55f5ed2e..b38358465d87 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -527,6 +527,24 @@ static void sun6i_dsi_setup_format(struct sun6i_dsi *dsi,
>  		     SUN6I_DSI_PIXEL_CTL0_FORMAT(fmt));
>  }
>  
> +static u16 sun6i_dsi_get_timings_vblk(struct sun6i_dsi *dsi,
> +				      struct drm_display_mode *mode, u16 hblk)
> +{
> +	struct mipi_dsi_device *device = dsi->device;
> +	unsigned int Bpp = mipi_dsi_pixel_format_to_bpp(device->format) / 8;
> +	int tmp;
> +
> +	/*
> +	 * The vertical blank is set using a blanking packet (4 bytes +
> +	 * payload + 2 bytes). Its minimal size is therefore 6 bytes
> +	 */
> +#define VBLK_PACKET_OVERHEAD	6
> +	tmp = (mode->htotal * Bpp) * mode->vtotal -
> +	      (hblk + VBLK_PACKET_OVERHEAD);
> +
> +	return (device->lanes - tmp % device->lanes);

This should have a comment explaining why it's needed

> +}
> +
>  static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
>  				    struct drm_display_mode *mode)
>  {
> @@ -586,13 +604,8 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
>  			   (mode->htotal - (mode->hsync_end - mode->hsync_start)) * Bpp -
>  			   HBLK_PACKET_OVERHEAD);
>  
> -		/*
> -		 * And I'm not entirely sure what vblk is about. The driver in
> -		 * Allwinner BSP is using a rather convoluted calculation
> -		 * there only for 4 lanes. However, using 0 (the !4 lanes
> -		 * case) even with a 4 lanes screen seems to work...
> -		 */
> -		vblk = 0;
> +		if (device->lanes == 4)

And that can be done in the function itself.

Maxime

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

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