linux-kernel - Re: [RESEND PATCH] drm/rockchip: dsi: move all lane config except LCDC mux to bind()

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Date:   Wed, 5 May 2021 23:53:07 +1000
From:   Jonathan Liu <net147@...il.com>
To:     Thomas Hebb <tommyhebb@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Nickey Yang <nickey.yang@...k-chips.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Brian Norris <briannorris@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Sandy Huang <hjc@...k-chips.com>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-rockchip@...ts.infradead.org
Subject: Re: [RESEND PATCH] drm/rockchip: dsi: move all lane config except
 LCDC mux to bind()

On Mon, 19 Apr 2021 at 02:04, Thomas Hebb <tommyhebb@...il.com> wrote:
>
> When we first enable the DSI encoder, we currently program some per-chip
> configuration that we look up in rk3399_chip_data based on the device
> tree compatible we match. This data configures various parameters of the
> MIPI lanes, including on RK3399 whether DSI1 is slaved to DSI0 in a
> dual-mode configuration. It also selects which LCDC (i.e. VOP) to scan
> out from.
>
> This causes a problem in RK3399 dual-mode configurations, though: panel
> prepare() callbacks run before the encoder gets enabled and expect to be
> able to write commands to the DSI bus, but the bus isn't fully
> functional until the lane and master/slave configuration have been
> programmed. As a result, dual-mode panels (and possibly others too) fail
> to turn on when the rockchipdrm driver is initially loaded.
>
> Because the LCDC mux is the only thing we don't know until enable time
> (and is the only thing that can ever change), we can actually move most
> of the initialization to bind() and get it out of the way early. That's
> what this change does. (Rockchip's 4.4 BSP kernel does it in mode_set(),
> which also avoids the issue, but bind() seems like the more correct
> place to me.)
>
> Tested on a Google Scarlet board (Acer Chromebook Tab 10), which has a
> Kingdisplay KD097D04 dual-mode panel. Prior to this change, the panel's
> backlight would turn on but no image would appear when initially loading
> rockchipdrm. If I kept rockchipdrm loaded and reloaded the panel driver,
> it would come on. With this change, the panel successfully turns on
> during initial rockchipdrm load as expected.
>
> Fixes: 2d4f7bdafd70 ("drm/rockchip: dsi: migrate to use dw-mipi-dsi bridge driver")
> Signed-off-by: Thomas Hebb <tommyhebb@...il.com>

Tested-by: Jonathan Liu <net147@...il.com>

Fixes MIPI-DSI panel initialization for me on RK3399 too.

Regards,
Jonathan