On 11/24/2014 03:00 PM, Laurent Pinchart wrote: > Hi Daniel, > > (CC'ing Rob Clark and Lars-Peter. As a reminder we're discussing the "drm: > Decouple EDID parsing from I2C adapter" patch available at > git://linuxtv.org/pinchartl/fbdev.git drm/next/du) > > On Monday 24 November 2014 14:09:39 Daniel Vetter wrote: >> On Mon, Nov 24, 2014 at 11:46:18AM +0200, Laurent Pinchart wrote: >>>> - the interface looks rather backwards: Either this still does i2c >>>> reads, and then you'd just need a i2c-over-whatever adapter to make it >>>> work. Or you have other magic means to optain an edid block, in which >>>> case just do that and then feed the edid drm_add_edid_modes. >>> >>> I have a magic way to get EDID over I2C :-) Basically the ADV7511 controls >>> the DDC bus, and exposes EDID data over I2C using vendor commands. To >>> read an EDID block I have to write an ADV7511 register over I2C with the >>> block number, wait for an interrupt, read a status register to check >>> whether EDID data is available or whether an error occurred, and then >>> read EDID data from the ADV7511 over I2C in 64-bytes chunks. This needs >>> to be repeated for every block. I thus can't use drm_get_edid() directly. >> >> Sounds familiar. See the special ddc-over-sdvo i2c bus we register in >> intel_sdvo.c, specifically look at intel_sdvo_init_ddc_proxy. It is a bit >> of boilerplate, but in the end just amounts to 3 small functions and one >> tiny vtable to wire it all up cleanly. > > That's what I would have done as well if I had a device-specific I2C adapter > connected to the DDC bus, but in this case the interface exposed by the > ADV7511 to the SoC over I2C consists of higher level device-specific I2C > commands to read EDID data. There is no low-level I2C read/write primitives > available. I would thus need to expose a fake adapter that would receive I2C > commands, parse them to detect an EDID block read, retrieve the EDID data and > return them from the fake read. That doesn't make much sense to me.
The intel sdvo looks just like a simple I2C mux which will just pass-through messages from the master to the EDID EEPROM. The ADV7511 is unfortunately a bit different. You tell it to fetch the EDID information, then it will do some magic and then you can read the EDID back. Abstracting this as a this as a I2C controller will, while possible, result in a fair amount of boiler plate code that will not look particularly pretty. - Lars
