linux-kernel - Re: [PATCH V2 1/6] drm: bridge: samsung-dsim: fix blanking packet size calculation

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Message-ID: <CAMty3ZCn9_AT8SOfFD-MYox16ZcqOEezt_0x6aES6LWQFj8Kpg@mail.gmail.com>
Date:   Mon, 24 Apr 2023 14:33:38 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Adam Ford <aford173@...il.com>, l.stach@...gutronix.de
Cc:     dri-devel@...ts.freedesktop.org, m.szyprowski@...sung.com,
        aford@...conembedded.com, dario.binacchi@...rulasolutions.com,
        Inki Dae <inki.dae@...sung.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Marek Vasut <marex@...x.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 1/6] drm: bridge: samsung-dsim: fix blanking packet
 size calculation

On Sun, Apr 23, 2023 at 5:42 PM Adam Ford <aford173@...il.com> wrote:
>
> From: Lucas Stach <l.stach@...gutronix.de>
>
> Scale the blanking packet sizes to match the ratio between HS clock
> and DPI interface clock. The controller seems to do internal scaling
> to the number of active lanes, so we don't take those into account.
>
> Signed-off-by: Lucas Stach <l.stach@...gutronix.de>
> Signed-off-by: Adam Ford <aford173@...il.com>
> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index e0a402a85787..2be3b58624c3 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -874,17 +874,29 @@ static void samsung_dsim_set_display_mode(struct samsung_dsim *dsi)
>         u32 reg;
>
>         if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> +               int byte_clk_khz = dsi->burst_clk_rate / 1000 / 8;
> +               int hfp = (m->hsync_start - m->hdisplay) * byte_clk_khz / m->clock;

I do not quite understand why it depends on burst_clk_rate, would you
please explain? does it depends on bpp something like this

mipi_dsi_pixel_format_to_bpp(format) / 8

> +               int hbp = (m->htotal - m->hsync_end) * byte_clk_khz / m->clock;
> +               int hsa = (m->hsync_end - m->hsync_start) * byte_clk_khz / m->clock;
> +
> +               /* remove packet overhead when possible */
> +               hfp = max(hfp - 6, 0);
> +               hbp = max(hbp - 6, 0);
> +               hsa = max(hsa - 6, 0);

6 blanking packet overhead here means, 4 bytes + payload + 2 bytes
format? does this packet overhead depends on the respective porch's
like hpf, hbp and hsa has different packet overheads?

Jagan.