On 11/12/2015 07:20 PM, Emil Velikov wrote:
On 12 November 2015 at 13:18, Thierry Reding thierry.reding@gmail.com wrote:
On Thu, Nov 12, 2015 at 12:48:51PM +0000, Emil Velikov wrote:
Hello Thierry, all,
Inspired by a recent discussion I was started wondering - where is the cut between DRM i2c modules (most of which encoders/transmitters) and bridge drivers (again some of which i2c encoders) ? Does anyone has some pointers on the topic ?
DRM bridge is a superset of I2C encoders, so everything that I2C encoder drivers do they should be able to do with DRM bridges, and more. There isn't a strict guideline here, but I think there's general agreement that new drivers should be using the DRM bridge framework. The primary reason is that bridges integrate seamlessly with the driver model, that is, the drivers that implement them are regular drivers that register with the corresponding bus and get bound to a device, whereas the I2C encoder infrastructure is mostly about manually instantiating devices.
For existing drivers I guess they could all be converted, but doing so may require a bit of work. They also tend to work as-is, so finding volunteers to do the conversion is probably going to be difficult given the lack of motivation.
Thierry
Based on the above I did a very quick search for third party IP modules in the DRM subsystem:
- i915
dvo_ch7017.c dvo_ch7xxx.c dvo_ivch.c dvo_ns2501.c dvo_sil164.c dvo_tfp410.c
It looks like these use some framework that's custom to the i915 driver but could otherwise easily be DRM bridges.
- gma500
tc35876x-dsi-lvds.c
This seems to be some sort of hybrid bridge and panel driver.
- sti
sti_hdmi_tx3g0c55phy.c sti_hdmi_tx3g4c28phy.c
These seem to implement some sort of PHY interface, but from a quick look moving these to the PHY framework seems overkill. They seem no good fit for DRM bridge because they are not separate devices, but rather the SoC generation specific bits of the STi HDMI driver.
(and for posterity)
- i2c
adv7511.c ch7006_drv.c sil164_drv.c tda998x_drv.c
- bridge
dw_hdmi.c nxp-ptn3460.c parade-ps8622.c
By the looks of it, we can move rework (some of?) the above into i2c/bridge modules and in other cases (sil164) just use the existing one ? I'm neither volunteering nor suggesting people must work of these, merely curious.
My take on this is that it's probably best to keep the above in their current form. If they need to be shared across multiple hardware setups it might make sense to convert them to DRM bridge drivers.
For new drivers it's probably best to make them bridge drivers from the start.
Thanks for the comprehensive reply Thierry. Pretty sure there are other people wondering about these - this should straighten things out.
Please refer to the following thread for a similar discussion:
http://lists.freedesktop.org/archives/dri-devel/2015-July/087097.html
Just a small note: considering that most desktop GPUs are moving (have moved ?) away from third party encoders/transmitters I doubt we'll be seeing any movements on that front.
We still have a requirement for such encoders in the SoC world. A SoC may provide a particular kind of encoder output, but we might need to convert that into another type of encoded output. There are multiple reasons why we might want to do this (SoC limitations, support old encoded formats like LVDS, weird requirements on some boards).
There is also a trend of re-use of the same third party encoder IPs across multiple SoCs. Having bridges for such IPs is helpful too.
Archit
Cheers, Emil _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel