linux-kernel - Re: [linux-sunxi] [PATCH 2/3] drm/sun4i: dsi: fix DRQ calculation

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Date:   Thu, 3 Oct 2019 10:07:13 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     Maxime Ripard <mripard@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] [PATCH 2/3] drm/sun4i: dsi: fix DRQ calculation

Hi,

On Tue, Oct 1, 2019 at 1:34 PM Icenowy Zheng <icenowy@...c.io> wrote:
>
> According to the BSP source code, when calculating the magic DRQ value
> outside burst mode, a formula of "lcd_ht - lcd_x - lcd_hbp", which is
> interpreted as right margin (HFP value). However, currently the
> sun6i_mipi_dsi driver code calculates it wrongly as HFP + sync length,
> which lead to timing error.
>
> Fix the DRQ calculation by change it to use HFP.
>
> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
> ---
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> index c86e11631ebc..2d3e822a7739 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -436,9 +436,9 @@ static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
>                              SUN6I_DSI_BURST_LINE_SYNC_POINT(SUN6I_DSI_SYNC_POINT));
>
>                 val = SUN6I_DSI_TCON_DRQ_ENABLE_MODE;
> -       } else if ((mode->hsync_end - mode->hdisplay) > 20) {
> +       } else if ((mode->hsync_start - mode->hdisplay) > 20) {
>                 /* Maaaaaagic */
> -               u16 drq = (mode->hsync_end - mode->hdisplay) - 20;
> +               u16 drq = (mode->hsync_start - mode->hdisplay) - 20;

I have similar patch in the ML, which required commit details
commented by Chen-Yu [1]. So, I'm trying to send it accordingly, let
me know if you have issues.

[1] https://patchwork.freedesktop.org/patch/305920/