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

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Message-ID: <1485869700.2932.57.camel@pengutronix.de>
Date:   Tue, 31 Jan 2017 14:35:00 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Steve Longerbeam <slongerbeam@...il.com>,
        Hans Verkuil <hverkuil@...all.nl>, robh+dt@...nel.org,
        mark.rutland@....com, shawnguo@...nel.org, kernel@...gutronix.de,
        fabio.estevam@....com, mchehab@...nel.org, nick@...anahar.org,
        markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, bparrot@...com,
        geert@...ux-m68k.org, arnd@...db.de, sudipm.mukherjee@...il.com,
        minghsiu.tsai@...iatek.com, tiffany.lin@...iatek.com,
        jean-christophe.trotin@...com, horms+renesas@...ge.net.au,
        niklas.soderlund+renesas@...natech.se, robert.jarzmik@...e.fr,
        songjun.wu@...rochip.com, andrew-ct.chen@...iatek.com,
        gregkh@...uxfoundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-media@...r.kernel.org, devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v3 00/24] i.MX Media Driver

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