linux-kernel - Re: [PATCH] video: fbdev: mxsfb: fix pixelclock polarity

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Date:	Fri, 06 May 2016 13:29:59 -0700
From:	Stefan Agner <stefan@...er.ch>
To:	plagnioj@...osoft.com, shawnguo@...nel.org
Cc:	s.hauer@...gutronix.de, Ying.Liu@...escale.com,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	LW@...o-electronics.de, fabio.estevam@...escale.com,
	max.krummenacher@...adex.com
Subject: Re: [PATCH] video: fbdev: mxsfb: fix pixelclock polarity

Hi Shawn,

On 2016-01-25 17:29, Stefan Agner wrote:
> The PIXDATA flags of the display_flags enum are controller centric,
> e.g. NEGEDGE means the controller shall drive the data signals on
> pixelclocks negative edge. However, the drivers flag is display
> centric: Sample the data on negative (falling) edge.
> 
> Therefore, change the if statement to check for the POSEDGE flag
> (which is typically not set):
> Drive on positive edge => sample on negative edge

Any comment on that patch?

--
Stefan


> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
> Hi all
> 
> Shawn, I would like to have at least your Ack on this before merge.
> 
> It seems that this has been wrong since the driver is able to use
> the timings from the device tree, introduced with 669406534b4a
> ("video: mxsfb: get display timings from device tree").
> 
> Not sure how many device trees actually specify the wrong pixel clock
> polarity due to that. At least the initial flag convertion from the
> old platform data structures done with 0d9f8217db15 ("ARM: mxs: move
> display timing configurations into device tree") seems to be affected
> and would need to be changed accordingly...
> 
> Not sure how we should handle this, maybe just invert all
> pixelclk-active properties where the mxsfb driver is in use...?
> 
> --
> Stefan
> 
>  drivers/video/fbdev/mxsfb.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/video/fbdev/mxsfb.c b/drivers/video/fbdev/mxsfb.c
> index 4e6608c..38898a9 100644
> --- a/drivers/video/fbdev/mxsfb.c
> +++ b/drivers/video/fbdev/mxsfb.c
> @@ -150,7 +150,7 @@
>  #define STMLCDIF_24BIT 3 /** pixel data bus to the display is of 24
> bit width */
>  
>  #define MXSFB_SYNC_DATA_ENABLE_HIGH_ACT	(1 << 6)
> -#define MXSFB_SYNC_DOTCLK_FALLING_ACT	(1 << 7) /* negtive edge sampling */
> +#define MXSFB_SYNC_DOTCLK_FALLING_ACT	(1 << 7) /* negative edge sampling */
>  
>  enum mxsfb_devtype {
>  	MXSFB_V3,
> @@ -788,7 +788,16 @@ static int mxsfb_init_fbinfo_dt(struct mxsfb_info *host,
>  
>  	if (vm.flags & DISPLAY_FLAGS_DE_HIGH)
>  		host->sync |= MXSFB_SYNC_DATA_ENABLE_HIGH_ACT;
> -	if (vm.flags & DISPLAY_FLAGS_PIXDATA_NEGEDGE)
> +
> +	/*
> +	 * The PIXDATA flags of the display_flags enum are controller
> +	 * centric, e.g. NEGEDGE means drive data on negative edge.
> +	 * However, the drivers flag is display centric: Sample the
> +	 * data on negative (falling) edge. Therefore, check for the
> +	 * POSEDGE flag:
> +	 * drive on positive edge => sample on negative edge
> +	 */
> +	if (vm.flags & DISPLAY_FLAGS_PIXDATA_POSEDGE)
>  		host->sync |= MXSFB_SYNC_DOTCLK_FALLING_ACT;
>  
>  put_display_node: