Hi Marek,
On 04.12.2024 00:40, Marek Vasut wrote:
On 12/3/24 8:20 AM, Nikolaus Voss wrote:
On 03.12.2024 04:12, Marek Vasut wrote:
On 12/3/24 3:22 AM, Liu Ying wrote:
[...]
I doubt that pixel clock tree cannot find appropriate division
ratios
for some pixel clock rates, especially for dual-link LVDS on
i.MX8MP
and i.MX93 platforms, because PLL clock rate should be 7x faster
than
pixel clock rate and 2x faster than "ldb" clock rate so that the
3.5
folder between "ldb" clock and pixel clock can be met. That means
the
PLL clock rate needs to be explicitly set first for this case.
Can you assign the PLL clock rate in DT to satisfy the "ldb" and
pixel
clock rates like the below commit does, if you use a LVDS panel?
4fbb73416b10 ("arm64: dts: imx8mp-phyboard-pollux: Set Video PLL1
frequency to 506.8 MHz")
I probably could. The point of my patch is you don't have to know
in
advance which LVDS panel is connected, and you don't have to
calculate
the base PLL clock by hand and store it in the device tree.
In my test system, I have three different LVDS panels with EDID
EEPROM,
none of which worked with the stock driver, but all work with this
patch.
With slightly adapted pixel clocks though.
If each of the three LVDS panels has only one display mode, you may
assign the PLL clock rates in DT overlays for the panels.
I temporarily agree.
I also currently use DTOs for various panels including their PLL
setting, but in the end, I think/hope the work of Miquel and co. is
going to make that PLL setting part unnecessary.
That is exactly what my patch is about. I want to use one DT for all
panels
Right
and store the panel's timing in EDID EEPROM.
Oh, that is a new one. Does the EDID EEPROM store the entirety of
'struct display_timing {}' somehow , or is that a custom format ?
Well, sort of ;-). VESA has taken care of this 30 years ago
(https://en.wikipedia.org/wiki/Extended_Display_Identification_Data).
DRM handles this with drm_get_edid() and siblings, e.g. :
@@ -86,16 +92,36 @@ static int panel_lvds_get_modes(struct drm_panel
*panel,
{
struct panel_lvds *lvds = to_panel_lvds(panel);
struct drm_display_mode *mode;
+ int num = 0;
+
+ /* probe EDID if a DDC bus is available */
+ if (lvds->ddc) {
+ pm_runtime_get_sync(lvds->dev);
+
+ if (!lvds->edid)
+ lvds->edid = drm_get_edid(connector, lvds->ddc);
+
+ if (lvds->edid)
+ num += drm_add_edid_modes(connector,
lvds->edid);
+
+ pm_runtime_mark_last_busy(lvds->dev);
+ pm_runtime_put_autosuspend(lvds->dev);
+ }
panel-simple.c does that in mainline, I added it to panel-lvds.c.
The kernel subdir tools/edid has some code to generate the EEPROM data
from timings and flags.
We keep the DDC EEPROM on a small adapter glued to to back of the panel
so we can replace the usually short-lived panel with a successor.
--
Nikolaus Voss
