linux-kernel - Re: [PATCH v2] drm/mxsfb: fix pixel clock polarity

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Message-ID: <eb31ad83-eecd-3ac3-84a0-a09d523107c7@denx.de>
Date:   Wed, 14 Dec 2016 22:25:07 +0100
From:   Marek Vasut <marex@...x.de>
To:     Stefan Agner <stefan@...er.ch>
Cc:     airlied@...ux.ie, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/mxsfb: fix pixel clock polarity

On 12/14/2016 09:48 PM, Stefan Agner wrote:
> The DRM subsystem specifies the pixel clock polarity from a
> controllers perspective: DRM_BUS_FLAG_PIXDATA_NEGEDGE means
> the controller drives the data on pixel clocks falling edge.
> That is the controllers DOTCLK_POL=0 (Default is data launched
> at negative edge).
> 
> Also change the data enable logic to be high active by default
> and only change if explicitly requested via bus_flags. With
> that defaults are:
> - Data enable: high active
> - Pixel clock polarity: controller drives data on negative edge
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>

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

> ---
> Changes since v1:
> - Improved comments/fixed typo
> 
>  drivers/gpu/drm/mxsfb/mxsfb_crtc.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> index 3770dd2..5556e53 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> @@ -195,9 +195,16 @@ static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
>  		vdctrl0 |= VDCTRL0_HSYNC_ACT_HIGH;
>  	if (m->flags & DRM_MODE_FLAG_PVSYNC)
>  		vdctrl0 |= VDCTRL0_VSYNC_ACT_HIGH;
> -	if (bus_flags & DRM_BUS_FLAG_DE_HIGH)
> +	/* Make sure Data Enable is high active by default */
> +	if (!(bus_flags & DRM_BUS_FLAG_DE_LOW))
>  		vdctrl0 |= VDCTRL0_ENABLE_ACT_HIGH;
> -	if (bus_flags & DRM_BUS_FLAG_PIXDATA_NEGEDGE)
> +	/*
> +	 * DRM_BUS_FLAG_PIXDATA_ defines are controller centric,
> +	 * controllers VDCTRL0_DOTCLK is display centric.
> +	 * Drive on positive edge       -> display samples on falling edge
> +	 * DRM_BUS_FLAG_PIXDATA_POSEDGE -> VDCTRL0_DOTCLK_ACT_FALLING
> +	 */
> +	if (bus_flags & DRM_BUS_FLAG_PIXDATA_POSEDGE)
>  		vdctrl0 |= VDCTRL0_DOTCLK_ACT_FALLING;
>  
>  	writel(vdctrl0, mxsfb->base + LCDC_VDCTRL0);
> 


-- 
Best regards,
Marek Vasut