Date:   Fri, 12 Jul 2019 08:15:32 +0000
From:   Robert Chiras <robert.chiras@....com>
To:     "agx@...xcpu.org" <agx@...xcpu.org>
CC:     dl-linux-imx <linux-imx@....com>, "marex@...x.de" <marex@...x.de>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
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Subject: Re: [EXT] Re: [PATCH 00/10] Improvements and fixes for mxsfb DRM
 driver

Hi Guido,

On Jo, 2019-07-11 at 17:04 +0200, Guido Günther wrote:
> Hi Robert,
> On Wed, Jun 26, 2019 at 04:32:08PM +0300, Robert Chiras wrote:
> > 
> > This patch-set improves the use of eLCDIF block on iMX 8 SoCs (like
> > 8MQ, 8MM
> > and 8QXP). Following, are the new features added and fixes from
> > this
> > patch-set:
> > 
> > 1. Add support for drm_bridge
> > On 8MQ and 8MM, the LCDIF block is not directly connected to a
> > parallel
> > display connector, where an LCD panel can be attached, but instead
> > it is
> > connected to DSI controller. Since this DSI stands between the
> > display
> > controller (eLCDIF) and the physical connector, the DSI can be
> > implemented
> > as a DRM bridge. So, in order to be able to connect the mxsfb
> > driver to
> > the DSI driver, the support for a drm_bridge was needed in mxsfb
> > DRM
> > driver (the actual driver for the eLCDIF block).
> So I wanted to test this but with both my somewhat cleaned up nwl
> driver¹ and the nwl driver forward ported from the nxp vendor tree
> I'm
> looking at a black screen with current mainline - while my dcss
> forward
> port gives me nice output on mipi dsi. Do you have a tree that uses
> mipi
> dsi on imx8mq where I could look at to check for differences?
Somewhere on the pixel path (between the display controller and the
DSI) there is a block that inverts the polarity. I can't remember
exactly what was the role of this block, but the polarity is inverted
when eLCDIF is used in combination with the DSI.
If you take a look at my DSI driver from NXP releases (I guess you have
them), you will see there is a hack in mode_fixup:

unsigned int *flags = &mode->flags;
if (dsi->sync_pol {
	*flags |= DRM_MODE_FLAG_PHSYNC;
	*flags |= DRM_MODE_FLAG_PVSYNC;
	*flags &= ~DRM_MODE_FLAG_NHSYNC;
	*flags &= ~DRM_MODE_FLAG_NVSYNC;
} else {
	*flags &= ~DRM_MODE_FLAG_PHSYNC;
	*flags &= ~DRM_MODE_FLAG_PVSYNC;
	*flags |= DRM_MODE_FLAG_NHSYNC;
	*flags |= DRM_MODE_FLAG_NVSYNC;
}

I know it's not clean, but it works for now. You can try this in your
driver and see if it helps.
These days I will also take your nwl-dsi driver and test it, and also
add support for bridge and eLCDIF to see if I can make it work.

Best regards,
Robert
> 
> Cheers,
>  -- Guido
> 
> > 
> > 
> > 2. Add support for additional pixel formats
> > Some of the pixel formats needed by Android were not implemented in
> > this
> > driver, but they were actually supported. So, add support for them.
> > 
> > 3. Add support for horizontal stride
> > Having support for horizontal stride allows the use of eLCDIF with
> > a GPU
> > (for example) that can only output resolution sizes multiple of a
> > power of
> > 8. For example, 1080 is not a power of 16, so in order to support
> > 1920x1080
> > output from GPUs that can produce linear buffers only in sizes
> > multiple to 16,
> > this feature is needed.
> > 
> > 3. Few minor features and bug-fixing
> > The addition of max-res DT property was actually needed in order to
> > limit
> > the bandwidth usage of the eLCDIF block. This is need on systems
> > where
> > multiple display controllers are presend and the memory bandwidth
> > is not
> > enough to handle all of them at maximum capacity (like it is the
> > case on
> > 8MQ, where there are two display controllers: DCSS and eLCDIF).
> > The rest of the patches are bug-fixes.
> > 
> > Mirela Rabulea (1):
> >   drm/mxsfb: Signal mode changed when bpp changed
> > 
> > Robert Chiras (9):
> >   drm/mxsfb: Update mxsfb to support a bridge
> >   drm/mxsfb: Update mxsfb with additional pixel formats
> >   drm/mxsfb: Fix the vblank events
> >   dt-bindings: display: Add max-res property for mxsfb
> >   drm/mxsfb: Add max-res property for MXSFB
> >   drm/mxsfb: Update mxsfb to support LCD reset
> >   drm/mxsfb: Improve the axi clock usage
> >   drm/mxsfb: Clear OUTSTANDING_REQS bits
> >   drm/mxsfb: Add support for horizontal stride
> > 
> >  .../devicetree/bindings/display/mxsfb.txt          |   6 +
> >  drivers/gpu/drm/mxsfb/mxsfb_crtc.c                 | 290
> > ++++++++++++++++++---
> >  drivers/gpu/drm/mxsfb/mxsfb_drv.c                  | 189
> > +++++++++++---
> >  drivers/gpu/drm/mxsfb/mxsfb_drv.h                  |  10 +-
> >  drivers/gpu/drm/mxsfb/mxsfb_out.c                  |  26 +-
> >  drivers/gpu/drm/mxsfb/mxsfb_regs.h                 | 128 ++++++---
> >  6 files changed, 531 insertions(+), 118 deletions(-)
> > 
> > --
> > 2.7.4
> > 
> > 
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