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

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Date:   Thu, 09 Nov 2017 14:34:06 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Stefan Agner <stefan@...er.ch>
Cc:     shawnguo@...nel.org, plagnioj@...osoft.com, 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,
        mauro.salvini@...group.net
Subject: Re: [PATCH] video: fbdev: mxsfb: fix pixelclock polarity

On Tuesday, October 17, 2017 06:01:58 PM Stefan Agner wrote:
> On 2017-10-17 15:56, Bartlomiej Zolnierkiewicz wrote:
> > Hi,
> > 
> > Stefan/Shawn:
> > 
> > Should I merge this patch? It seems to be still needed:
> > 
> > https://www.spinics.net/lists/linux-fbdev/msg23112.html
> 
> In my opinion yes, it fixes an issue... 
> 
> FWIW, I normally use the DRM driver when using mainline which does not
> suffer from this issue, so I did not mind much that this fix never made
> it...

I queued your patch (with Shawn's ACK) for 4.15, thanks!

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

> --
> Stefan
> 
> > 
> > Best regards,
> > --
> > Bartlomiej Zolnierkiewicz
> > Samsung R&D Institute Poland
> > Samsung Electronics
> > 
> > On Friday, May 06, 2016 01:29:59 PM Stefan Agner wrote:
> >> 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: