Re: [PATCH v3 00/24] i.MX Media Driver

[Philipp Zabel <p.zabel@pengutronix.de>]

On Tue, 2017-01-31 at 13:14 +0000, Russell King - ARM Linux wrote:
> On Tue, Jan 31, 2017 at 11:09:24AM +0100, Philipp Zabel wrote:
> > On Mon, 2017-01-30 at 13:06 +0000, Russell King - ARM Linux wrote:
> > > To help illustrate my point, consider the difference between
> > > MEDIA_BUS_FMT_RGB565_1X16 and MEDIA_BUS_FMT_RGB565_2X8_BE or
> > > MEDIA_BUS_FMT_RGB565_2X8_LE.  RGB565_1X16 means 1 pixel over an effective
> > > 16-bit wide bus (if it's not 16-bit, then it has to be broken up into
> > > separate "samples".)  RGB565_2X8 means 1 pixel as two 8-bit samples.
> > > 
> > > So, the 10-bit bayer is 1 pixel as 1.25 bytes.  Or is it, over a serial
> > > bus.  Using the RGB565 case, 10-bit bayer over a 4 lane CSI bus becomes
> > > interesting:
> > > 
> > > 	first byte	2nd	3rd
> > > lane 1	P0 9:2		S0	P7 9:2
> > > lane 2	P1 9:2		P4 9:2	S1
> > > lane 3	P2 9:2		P5 9:2	P8 9:2
> > > lane 4	P3 9:2		P6 9:2	P9 9:2
> > > 
> > > S0 = P0/P1/P2/P3 least significant two bits
> > > S1 = P4/P5/P6/P7 least significant two bits
> > > 
> > > or 2 lane CSI:
> > > 	first byte	2nd	3rd	4th	5th
> > > lane 1	P0 9:2		P2	S0	P5	P7
> > > lane 2	P1 9:2		P3	P4	P6	S1
> > > 
> > > or 1 lane CSI:
> > > lane 1	P0 P1 P2 P3 S0 P4 P5 P6 P7 S1 P8 P9 ...
> > 
> > These do look like three different media bus formats to me.
> 
> This isn't limited to the serial side - the parallel bus side between
> the CSI2 interface and CSI2IPU wrapper, and the CSI2IPU wrapper and
> the CS0/1 interfaces is much the same with 10-bit bayer.
> 
> Think of the CSI2 <-> CSI2IPU bit as the 4-lane case, lane 0 ending
> up on the least significant 8 bits of the 32-bit bus, lane 3 on the
> top 8-bits.
> 
> Post CSI2IPU, it talks about a 16-bit bus in the diagrams, so that's
> kind of the 2-lane case above...

You are right, on the parallel buses the format most definitely is not
MEDIA_BUS_FMT_SBGGR10_1X10. We don't have any representation of the
32-bit bus between CSI2 host and CSI2IPU gasket because we model the two
as a single entity, but the four 16-bit parallel buses between the
CSI2IPU gasket and the IPU1/2 CSI0/1 probably should be set to a custom
format describing this accurately.

regards
Philipp