Hi Maxime, On Tue, Jul 07, 2026 at 11:01:43AM +0300, Laurent Pinchart wrote: > On Tue, Jul 07, 2026 at 09:46:52AM +0200, Maxime Ripard wrote: > > On Mon, Jul 06, 2026 at 07:02:43PM +0300, Laurent Pinchart wrote: > > > 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. > > > > What's the expected user-experience for someone with that board > > unplugging a display and plugging another then? Update the device tree, > > rebuild it, rebuild the firmware and / or resign it and reboot? > > The whole point is that they can't easily unplug the display. This patch > series is meant to support devices where the display is an integral part > of the device. The user experience is expected to be the same as for a > user who will take a phone, remove the display panel, and plug a > different one. It's certainly possible, and they would have to update > the DT indeed. > > > That doesn't sound very practical, and even impossible in some cases. > > > > > > 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. > > > > How is that not helping? Your problem is that you have a display you > > can't get the supported resolutions from. What I'm suggesting allows you > > to create all the possible resolutions for that display, allowing the > > user to use the display, which is what we did for multiple drivers with > > the same problem. > > How would the possible resolutions be provided to the kernel ? Isn't it > the whole point of EDID ? > > > You seem to be set on providing the EDID to the kernel, but it's a > > terrible idea to begin with, so I'd rather discuss alternatives. > > Could you elaborate on why it is a terrible idea ?
I'd be happy to continue this discussion when you'll have time. -- Regards, Laurent Pinchart
