From: Stefan Agner <stefan@agner.ch>
To: marex@denx.de
Cc: airlied@linux.ie, dri-devel@lists.freedesktop.org,
linux-kernel@vger.kernel.org, Stefan Agner <stefan@agner.ch>
Subject: [PATCH] drm/mxsfb: fix pixel clock polarity
Date: Wed, 7 Dec 2016 16:27:06 -0800 [thread overview]
Message-ID: <20161208002706.10147-1-stefan@agner.ch> (raw)
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@agner.ch>
---
Hi Marek,
I discovered this while testing on a i.MX 7 eLCDIF IP. Particularly the
non-standard DE polarity was causing issues. I was using a EDT display
which is part of simple panel driver since a while now and does not
specify any bus_flags currently... Of course I could (and probably should)
add the proper bus_flags there too, but there are several displays
which do not specify any polarity and likely rely on sensible driver
standards (which is afact high active for the DE signal).
--
Stefan
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 0818903..4bcc8a3 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
@@ -168,9 +168,16 @@ 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)
+ /* Data Enable should be 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)
+ /*
+ * Note: DRM_BUS_FLAG_PIXDATA defines are controller centric,
+ * controllers VDCTRL0_DOTCLK is display centric.
+ * Drive on positive edige -> 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);
--
2.10.2
next reply other threads:[~2016-12-08 0:27 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 0:27 Stefan Agner [this message]
2016-12-08 0:49 ` [PATCH] drm/mxsfb: fix pixel clock polarity Marek Vasut
2016-12-08 0:59 ` Stefan Agner
2016-12-08 1:26 ` Stefan Agner
2016-12-08 2:37 ` Marek Vasut
2016-12-08 20:46 ` Stefan Agner
2016-12-08 23:38 ` Marek Vasut
2016-12-14 0:01 ` Stefan Agner
2016-12-14 8:04 ` Marek Vasut
2016-12-14 20:29 ` Stefan Agner
2016-12-14 20:38 ` Marek Vasut
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20161208002706.10147-1-stefan@agner.ch \
--to=stefan@agner.ch \
--cc=airlied@linux.ie \
--cc=dri-devel@lists.freedesktop.org \
--cc=linux-kernel@vger.kernel.org \
--cc=marex@denx.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).