On 25/02/2020 17:01, Laurent Pinchart wrote:
Hi Sebastian,
Thank you for the patch.
On Tue, Feb 25, 2020 at 12:20:40AM +0100, Sebastian Reichel wrote:
This drops the virtual channel logic. Afterwards DSI clients
request their channel number and get the virtual channel with
the same number or -EBUSY if already in use.
I wonder why this level of indirection was used, allocating "virtual
VCs". A single virtual indirection should be enough :-) I may be missing
some context though, I'll defer that to Tomi, but for me,
I haven't reviewed the code yet, and it's been a long time since I wrote this code. But maybe this
explains at least some:
(I hope I remember this right)
DSI packets have virtual channel IDs (VCID). That's number 0-3 that needs to be in the packets.
DSI IP has virtual channel "blocks" (VC), with associated registers. So 4 VC register blocks. These
are not related to DSI virtual channel IDs in any way.
To do DSI transactions, you choose a VC, and program it. A VC can send data via video pipeline, or
transmit and receive data messages created with CPU. And in both cases, you need to include the VCID
in the transmissions, of course.
So, I think a normal use case could be a single panel, with VCID 0. To send video data and control
messages, you would use VC0 and VC1. VC0 would be configured for video data, and VC1 would be
configured for control messages.
And if I recall right, currently you first request a free VC from the IP with request_vc(). Then you
use set_vc_id(channel, id) to set the VCID, used when doing transactions with that VC.
So the virtual channel naming is pretty confusing in the DSI IP, in my opinion.
Tomi
--
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
