Hi, On Mon, Jul 22, 2019 at 1:24 PM Sean Paul <sean@xxxxxxxxxx> wrote: > > On Mon, Jul 22, 2019 at 11:19:45AM -0700, Matthias Kaehlcke wrote: > > The DDC/CI protocol involves sending a multi-byte request to the > > display via I2C, which is typically followed by a multi-byte > > response. The internal I2C controller only allows single byte > > reads/writes or reads of 8 sequential bytes, hence DDC/CI is not > > supported when the internal I2C controller is used. The I2C > > This is very likely a stupid question, but I didn't see an answer for it, so > I'll just ask :) > > If the controller supports xfers of 8 bytes and 1 bytes, could you just split > up any of these transactions into len/8+len%8 transactions? It's not quite that easy, I think. Specifically a 1-byte transfer isn't really a 1-byte transfer. It always sticks this on the wire for a 1-byte write: Start Slave address (7 bits) + write (1 bit) (wait ack) Register address 1 byte of data wait for ack Stop ...or for a 1-byte read: Start Slave address (7 bits) + write (1 bit) (wait ack) Register address (wait ack) Repeated Start (1 bit) Slave address (7 bits) + read (1 bit) (read 1 byte of data) Ack Stop Putting more than one of those in a row is not the same thing as just doing a whole bunch of reads or a whole bunch of writes with no "stop" in between. As far as I could find out about DDC/CI it's part of the spec to _not_ send the stop between the reads / writes. -Doug _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
