Hi Tomi, On Fri, May 03, 2019 at 02:43:51PM +0300, Tomi Valkeinen wrote: > On 23/04/2019 17:56, Laurent Pinchart wrote: > > >> During initial driver development I had one eDP display that reports 0 in Bit 0 > >> (ANSI 8B/10B) of DPCD reg 0x0006 (MAIN_LINK_CHANNEL_CODING). > >> Also it does not react on setting Bit 0 (SET_ANSI 8B10B) in 0x0108 > >> (MAIN_LINK_CHANNEL_CODING_SET) - after reading back it was 0 again. > >> So I had to disable 8B10 encoding on tc358767 side to make this display > >> work. > > > > Out of curiosity, how does the eDP display recover the clock without > > 8B/10B encoding ? > > > >> On other hand if there are displays that report zero bit 0 in > >> MAIN_LINK_CHANNEL_CODING while needing 8b10b then this patch looks > >> reasonable. > >> > >> May be driver should read back MAIN_LINK_CHANNEL_CODING_SET > >> register after setting it and check if 8b10b actually enabled? > > > > This sounds like a reasonable thing to try. Tomi, do you still have > > accesss to those faulty monitors ? > > On my monitor it does not seem to matter whether I write 0 or 1 to > MAIN_LINK_CHANNEL_CODING_SET, as long as I have 8b10b enabled on > TC358767 side. The writes do go through, and I can read the written bit > back. > > So... I guess when we talk about eDP panels, there may be all kinds of > oddities, as they're usually meant to be used with a certain configuration. > > But if everyone agrees that 8B10B is a normal, required feature of DP, > and there is an eDP panel that needs 8B10B disabled, maybe that panel > has to be handled separately as a special case? A dts entry to disable > 8B10B? Or something. But it does not sound like a good idea for the > driver to try to guess this. As reported by Andrey, there is at least one panel that would break with this patch. I agree 8b10b should be the default, but if the above procedure works for all the panels we know about, is there an issue implementing it ? -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
