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SubjectRe: [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@amarulasolutions.com>
> Tested-by: Merlijn Wajer <merlijn@wizzup.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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