search

beagleboard / linux

The official Read Only BeagleBoard and BeagleBone kernel repository https://git.beagleboard.org/beagleboard/linux
http://beagleboard.org/source
Other
715 stars 566 forks source link

Why can only "nxp,tda998x" be used ? #191

Closed Pillar1989 closed 4 years ago

Pillar1989 commented 5 years ago

https://github.com/beagleboard/linux/blob/83521bea4e860954320fc0ee491c7e2084f22aec/drivers/gpu/drm/tilcdc/tilcdc_external.c#L237-L240

A lot of people want to use SeeedStudio's high cost performance HDMI cape https://www.seeedstudio.com/SeeedStudio-BeagleBone-Green-HDMI-Cape-p-2570.html on the latest kernel, but because of this line of code, is not available

pdp7 commented 4 years ago

@Pillar1989 are you using a different HDMI chip than tda998x?

@RobertCElliott @jadonk is tda998x the only HDMI driver that is supported?

tilcdc_get_external_components() still does this in mainline: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/tilcdc/tilcdc_external.c#L174

    if (!of_device_is_compatible(node, "nxp,tda998x")) {
        of_node_put(node);
        return 0;
    }
Pillar1989 commented 4 years ago

@pdp7 The Linux kernel supports many LCD to HDMI chips. Obviously, it doesn't make sense to write code like this.

pdp7 commented 4 years ago

@Pillar1989 I discussed this with @RobertCNelson and he pointed out there is the Arrow BBB Industrial that uses adv7511 HDMI chip: https://github.com/beagleboard/BeagleBoard-DeviceTrees/blob/4a9c0a652f58090491319d27dac4bf76da7d6086/src/arm/am335x-abbbi.dts#L91

The "adv7511" is a proper "bridge" driver: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/bridge 4:30

While the "tda998x_drv.c" is a special... https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/i2c 4:31

The tda998x should be converted to a bridge driver, but no one's cared enough to change that. It's used on a lot of different arm boards.

Looking at the Seeed cape, I see it is using IT66121 HDMI Framer: https://wiki.seeedstudio.com/BeagleBone_Green_HDMI_Cape/

There was a patch to add it66121 driver to mainline posted by Phong LE in March 2020 that might be useful: https://lwn.net/Articles/814501/

In summary, tilcdc_get_external_components() in mainline does appear to be correct in that it is handling the the fact that tda998x is old and not covered by a real bridge driver.

Pillar1989 commented 4 years ago

Yes, I see. Thank you