On Mon, Jul 06, 2026 at 05:40:30PM +0200, Maxime Ripard wrote: > On Mon, Jul 06, 2026 at 12:45:22PM +0300, Laurent Pinchart wrote: > > On Mon, Jul 06, 2026 at 10:52:32AM +0200, Maxime Ripard wrote: > > > On Mon, Jul 06, 2026 at 12:35:39AM +0300, Laurent Pinchart wrote: > > > > Since DDC version 2, introduced in 1996, VGA monitors have exposed EDID > > > > data over an I2C bus. The bus is also used to detect the presence of a > > > > connected monitor by trying to read the EDID data. > > > > > > > > Some devices where the VGA display is integrated in the device and > > > > always connected do not connect the DDC pins. Some development boards, > > > > such as the Renesas M3N Salvator-XS, also do not connect the DDC pins. > > > > > > > > To support those, add the ability to provide hardcoded EDID data in the > > > > device tree. This is mutually exclusive with specifying a DDC bus, and > > > > can only be done when the VGA display is guaranteed to be always > > > > connected. > > > > > > > > Signed-off-by: Laurent Pinchart > > > > <[email protected]> > > > > > > This feels redundant with the EDID firmware loading mechanism we have in > > > KMS already. It should at least be mentioned why we would need to set it > > > in the device tree at all. > > > > Very good question. > > > > I assume you're talking about CONFIG_DRM_LOAD_EDID_FIRMWARE, as the > > debugfs override_edid feature isn't meant for production. If there are > > other relevant mechanisms I'm not aware of, please let me know. > > No, that's indeed what I meant. > > > In the use case at hand, the VGA display is an integral part of the > > device, the same way an LVDS or DSI panel would be. Using > > CONFIG_DRM_LOAD_EDID_FIRMWARE, the manufacturer would need to set the > > drm.edid_firmware command line parameter, and provide EDID as a file in > > /lib/firmware/ (possibly in an initramfs). Beside the complexity, and > > the fact it won't be very friendly to people who run a different > > userspace on the device, I think EDID counts in this case as system > > description, the same way we support specifying panel timings in device > > tree. > > It's *some* hardware description, but you have no idea whether it's > actually the hardware you're running from. What would be in that EDID > anyway?
It would be the EDID corresponding to the connected display :-) I see it as identical to how a user of the simple panel driver is responsible for listing the timings corresponding to the hardware in the device tree. > There's another alternative we've used several times already, in > simple-bridge for example: just register any VESA mode up to a given > resolution: > https://elixir.bootlin.com/linux/v7.1.2/source/drivers/gpu/drm/bridge/simple-bridge.c#L66 I don't see how that would help. The goal is to provide the kernel with the data corresponding to the display integrated in the device. > I guess it's what you would do with that EDID anyway? -- Regards, Laurent Pinchart
