linux-kernel - Re: [PATCH] drm: bridge: icn6211: Adjust clock phase using SYS_CTRL

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Date:   Mon, 23 May 2022 13:10:48 +0200
From:   Marek Vasut <marex@...x.de>
To:     Jonathan Liu <net147@...il.com>, dri-devel@...ts.freedesktop.org
Cc:     Maxime Ripard <maxime@...no.tech>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: bridge: icn6211: Adjust clock phase using SYS_CTRL_1

On 5/23/22 04:38, Jonathan Liu wrote:
> The code from [1] sets SYS_CTRL_1 to different values depending on the
> desired clock phase (0, 1/4, 1/2 or 3/4). A clock phase of 0 aligns the
> positive edge of the clock with the pixel data while other values delay
> the clock by a fraction of the clock period. A clock phase of 1/2 aligns
> the negative edge of the clock with the pixel data.
> 
> The driver currently hard codes SYS_CTRL_1 to 0x88 which corresponds to
> aligning the positive edge of the clock with the pixel data. This won't
> work correctly for panels that require aligning the negative edge of the
> clock with the pixel data.
> 
> Adjust the clock phase to 0 if DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE is
> present in bus_flags, otherwise adjust the clock phase to 1/2 as
> appropriate for DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE.
> 
> [1] https://github.com/tdjastrzebski/ICN6211-Configurator
> 
> Signed-off-by: Jonathan Liu <net147@...il.com>
> ---
>   drivers/gpu/drm/bridge/chipone-icn6211.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/chipone-icn6211.c b/drivers/gpu/drm/bridge/chipone-icn6211.c
> index 47dea657a752..df0290059aa3 100644
> --- a/drivers/gpu/drm/bridge/chipone-icn6211.c
> +++ b/drivers/gpu/drm/bridge/chipone-icn6211.c
> @@ -57,6 +57,10 @@
>   #define BIST_CHESS_XY_H		0x30
>   #define BIST_FRAME_TIME_L	0x31
>   #define BIST_FRAME_TIME_H	0x32
> +#define CLK_PHASE_0		0x88
> +#define CLK_PHASE_1_4		0x98
> +#define CLK_PHASE_1_2		0xa8
> +#define CLK_PHASE_3_4		0xb8
>   #define FIFO_MAX_ADDR_LOW	0x33
>   #define SYNC_EVENT_DLY		0x34
>   #define HSW_MIN			0x35
> @@ -414,7 +418,11 @@ static void chipone_atomic_enable(struct drm_bridge *bridge,
>   	chipone_configure_pll(icn, mode);
>   
>   	chipone_writeb(icn, SYS_CTRL(0), 0x40);
> -	chipone_writeb(icn, SYS_CTRL(1), 0x88);
> +
> +	if (bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE)
> +		chipone_writeb(icn, SYS_CTRL(1), CLK_PHASE_0);
> +	else
> +		chipone_writeb(icn, SYS_CTRL(1), CLK_PHASE_1_2);

Shouldn't both be "chipone_writeb(icn, SYS_CTRL(1), CLK_PHASE_0 | 0x8); 
and chipone_writeb(icn, SYS_CTRL(1), CLK_PHASE_1_2 | 0x8); respectively 
? I recall you mentioned that only the top two bits indicate the clock 
polarity , so the bottom 6 bits are something else ?

With that fixed:

Reviewed-by: Marek Vasut <marex@...x.de>

Thanks