On 10/17/22 05:54, Jagan Teki wrote:
On Sun, Oct 16, 2022 at 2:53 AM Marek Vasut <marex@xxxxxxx> wrote:
On 10/5/22 17:13, Jagan Teki wrote:
Look like an explicit fixing up of mode_flags is required for DSIM IP
present in i.MX8M Mini/Nano SoCs.
At least the LCDIF + DSIM needs active low sync polarities in order
to correlate the correct sync flags of the surrounding components in
the chain to make sure the whole pipeline can work properly.
On the other hand the i.MX 8M Mini Applications Processor Reference Manual,
Rev. 3, 11/2020 says.
"13.6.3.5.2 RGB interface
Vsync, Hsync, and VDEN are active high signals."
No clear evidence about whether it can be documentation issues or
something, so added a comment FIXME for this and updated the active low
sync polarities using SAMSUNG_DSIM_TYPE_IMX8MM hw_type.
[...]
+static int samsung_dsim_atomic_check(struct drm_bridge *bridge,
+ struct drm_bridge_state *bridge_state,
+ struct drm_crtc_state *crtc_state,
+ struct drm_connector_state *conn_state)
+{
+ struct samsung_dsim *dsi = bridge_to_dsi(bridge);
+ struct drm_display_mode *adjusted_mode = &crtc_state->adjusted_mode;
+
+ if (dsi->plat_data->hw_type == SAMSUNG_DSIM_TYPE_IMX8MM) {
+ /**
+ * FIXME:
+ * At least LCDIF + DSIM needs active low sync,
+ * but i.MX 8M Mini Applications Processor Reference Manual,
+ * Rev. 3, 11/2020 says
+ *
+ * 13.6.3.5.2 RGB interface
+ * Vsync, Hsync, and VDEN are active high signals.
+ */
+ adjusted_mode->flags |= (DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC);
+ adjusted_mode->flags &= ~(DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC);
+ }
It would be good to explain what exactly is going on here in the
comment, the comment says "Vsync, Hsync, and VDEN are active high
signals." and the code below does exact opposite and sets NxSYNC flags.
Yes, the MX8MM/MN does need HS/VS/DE active LOW, it is a quirk of that
MXSFB-DSIM glue logic. The MX8MP needs the exact opposite on all three,
active HIGH.
This is what exactly is mentioned in the comments.
2nd line mentioned the active low of signals.
+ * At least LCDIF + DSIM needs active low sync,
from 3rd line onwards it mentioned what reference manual is referring
Not quite understand what is misleading here.
This part:
"
+ * Vsync, Hsync, and VDEN are active high signals.
+ */
+ adjusted_mode->flags |= (DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC);
"
Comment claims the signals are active high by quoting datasheet, and
then sets the exact opposite on next line of code.
Have a look at this patch, I updated the comment there for MX8MP too:
[PATCH] drm: bridge: samsung-dsim: Add i.MX8M Plus support
