Re: [PATCH 2/2] drm/bridge/tc358775: Fix DSI clock division for vsync delay calculation

From: Vinay Simha B N <simhavcs@gmail.com>
To: Jiri Vanek <jirivanek1@gmail.com>
Cc: Jonas Karlman <jonas@kwiboo.se>, David Airlie <airlied@linux.ie>,
	Robert Foss <robert.foss@linaro.org>,
	"open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
	Neil Armstrong <narmstrong@baylibre.com>,
	open list <linux-kernel@vger.kernel.org>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Andrzej Hajda <a.hajda@samsung.com>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Subject: Re: [PATCH 2/2] drm/bridge/tc358775: Fix DSI clock division for vsync delay calculation
Date: Fri, 17 Jun 2022 10:03:40 +0530	[thread overview]
Message-ID: <CAGWqDJ6Boq5x4DofKx=US_Yx6_46JGTHuaLbEKq-uXRAz-35AA@mail.gmail.com> (raw)
In-Reply-To: <20220615222221.1501-3-jirivanek1@gmail.com>

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Reviewed-by: Vinay Simha BN <simhavcs@gmail.com>

On Thu, Jun 16, 2022 at 3:55 AM Jiri Vanek <jirivanek1@gmail.com> wrote:

> Use the same PCLK divide option (divide DSI clock to generate pixel clock)
> which is set to LVDS Configuration Register (LVCFG) also for a VSync delay
> calculation. Without this change an auxiliary variable could underflow
> during the calculation for some dual-link LVDS panels and then calculated
> VSync delay is wrong. This leads to a shifted picture on a panel.
>
> Tested-by: Jiri Vanek <jirivanek1@gmail.com>
> Signed-off-by: Jiri Vanek <jirivanek1@gmail.com>
> ---
>  drivers/gpu/drm/bridge/tc358775.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/tc358775.c
> b/drivers/gpu/drm/bridge/tc358775.c
> index cd2721ab02a9..fecb8558b49a 100644
> --- a/drivers/gpu/drm/bridge/tc358775.c
> +++ b/drivers/gpu/drm/bridge/tc358775.c
> @@ -430,7 +430,7 @@ static void tc_bridge_enable(struct drm_bridge *bridge)
>                 val = TC358775_VPCTRL_MSF(1);
>
>         dsiclk = mode->crtc_clock * 3 * tc->bpc / tc->num_dsi_lanes / 1000;
> -       clkdiv = dsiclk / DIVIDE_BY_3 * tc->lvds_link;
> +       clkdiv = dsiclk / (tc->lvds_link == DUAL_LINK ? DIVIDE_BY_6 :
> DIVIDE_BY_3);
>         byteclk = dsiclk / 4;
>         t1 = hactive * (tc->bpc * 3 / 8) / tc->num_dsi_lanes;
>         t2 = ((100000 / clkdiv)) * (hactive + hback_porch + hsync_len +
> hfront_porch) / 1000;
> --
> 2.30.2
>
>

-- 
regards,
vinaysimha

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