linux-kernel - Re: [PATCH v2] drm: bridge: icn6211: Adjust clock phase using SYS_CTRL

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Date:   Mon, 23 May 2022 15:15:47 +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 v2] drm: bridge: icn6211: Adjust clock phase using
 SYS_CTRL_1

On 5/23/22 15:01, 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>
> ---
> V2: Use GENMASK and FIELD_PREP macros
> ---
>   drivers/gpu/drm/bridge/chipone-icn6211.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/chipone-icn6211.c b/drivers/gpu/drm/bridge/chipone-icn6211.c
> index 47dea657a752..f1538fb5f8a9 100644
> --- a/drivers/gpu/drm/bridge/chipone-icn6211.c
> +++ b/drivers/gpu/drm/bridge/chipone-icn6211.c
> @@ -9,6 +9,8 @@
>   #include <drm/drm_print.h>
>   #include <drm/drm_mipi_dsi.h>
>   
> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
>   #include <linux/delay.h>
>   #include <linux/gpio/consumer.h>
>   #include <linux/i2c.h>
> @@ -26,6 +28,11 @@
>   #define PD_CTRL(n)		(0x0a + ((n) & 0x3)) /* 0..3 */
>   #define RST_CTRL(n)		(0x0e + ((n) & 0x1)) /* 0..1 */
>   #define SYS_CTRL(n)		(0x10 + ((n) & 0x7)) /* 0..4 */
> +#define SYS_CTRL_1_CLK_PHASE_MSK	GENMASK(5, 4)

This should be GENMASK(7, 6) , no ?