Re: [PATCH] video: fbdev: mxsfb: fix pixelclock polarity

[Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>]

Hi,

Stefan/Shawn:

Should I merge this patch? It seems to be still needed:

https://www.spinics.net/lists/linux-fbdev/msg23112.html

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@agner.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: