On 11/12/2015 07:20 PM, Emil Velikov wrote:
On 12 November 2015 at 13:18, Thierry Reding <thierry.reding@xxxxxxxxx> 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
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