On Fri, Jun 05, 2026 at 06:56:54PM +0200, Luca Ceresoli wrote: > On Fri Jun 5, 2026 at 6:09 PM CEST, Laurent Pinchart wrote: > > On Fri, Jun 05, 2026 at 05:18:43PM +0200, Luca Ceresoli wrote: > >> Hello Sean, > >> > >> +Cc Marek, Maxime. > >> > >> On Sat May 30, 2026 at 8:51 PM CEST, Sean Nyekjaer wrote: > >> > On Wed, May 27, 2026 at 02:27:36PM +0100, Sudarshan Shetty wrote: > >> >> The current DSI configuration enables MIPI_DSI_MODE_VIDEO_BURST. > >> >> while burst mode is supported by the hardware, its use > >> >> depends on continuous clock behavior from the DSI host. In practice, > >> >> burst mode may introduce instability depending on the host controller > >> >> implementation, as the DSI link may transition to low-power state > >> >> between bursts. > >> >> > >> >> Testing showed improved display stability when using non-burst mode on > >> >> affected panels. > >> >> > >> >> Remove MIPI_DSI_MODE_VIDEO_BURST and use non-burst video mode. > >> > > >> > We briefly talked about this at Embedded Recipes > >> > I promised to sent a link: > >> > https://lore.kernel.org/all/[email protected]/ > >> > >> Thanks for the discussion at ER and for this follow-up e-mail. > >> > >> > When burst mode is enabled, the LVDS clock gets way to high for my > >> > panel. I don't know if it's the DSI controller in the STM32MP1 or > >> > something not supported on the TI side. > >> > > >> > We have been running with this fix for 2 years :) > >> > >> If I can summarize the situation in the last 4 years: > >> > >> * Several users reported the same trouble > >> * Those users patch their kernel out of tree to disable burst mode as a > >> workaround > >> * According to Marek the correct way to make burst mode work is > >> implementing link negotiation > >> * Nobody is willing to implement link negotiation as of now > >> > >> And this leads me to some questions. > >> > >> * Do we want to keep the current situation (everybody beats their head on > >> the wall until they discover disabling burst mode "fixes" their panel, > >> and keep an out of tree patch)? > >> > >> * Assuming the priority is getting a screen working (and not saving power > >> on a black screen), would it make sense to apply this patch, and let > >> people improve in the future by implementing link negotiation? > >> > >> Let's pretend for a moment this is a new driver being developed: would > >> it be OK to have a basic working driver, without some power optimization > >> features which can be added later on? The only valid answer to this > >> question is obviously "yes". Doesn't the same principle apply here? If > >> it doesn't, why? > >> > >> * What is the expected power saving with burst mode? > >> > >> I'm afraid I don't have precise numbers but I measured the total board > >> consumption with or without burst mode (the former with a black screen > >> but backlight enabled) and found no difference: exactly 12.74 W in both > >> cases. > >> > >> Thanks for you rpatience in reading this. I hope it helps in finding a > >> better solution. > > > > Rephrasing this a bit, is the discussion about dropping support for a > > supported feature (burst mode) because users who suffer from the lack of > > another feature (link negotiation) are not willing to spend time > > implementing it, > > That's the question I have, more or less. I have no answer yet, I'm mostly > trying to clarify the situation in the first place, for myself and anyone > interested. > > Maybe it's worth pointing out that AFAICU any driver enabling burst mode is > buggy because in lack of link negotiation it may work or not, based on pure > luck. > > > and would prefer if users of burst mode were forced to > > do the work instead ? That doesn't seem very fair to me. > > Link negotiation is not just "another feature" w.r.t. burts mode. It's a > prerequisite for burst mode to work reliably. So hard-enabling burst mode > was building a roof without solid walls (link negotiation). > > So I'm rephrasing your the question :) as: shouldn't users of burst mode be > forced to implement link negotiation, since _they_ need it?
It's quite annoying when both positions have compelling arguments :-) Has anyone analyzed what work would be needed to implement the link negotiation ? Dropping burst mode without any plan to support it will be demotivating for some people. If asking for link negotiation support to support non-burst mode is too much yak shaving, would researching a technical plan be an acceptable middleground ? > Again: AFAICU, I'm trying to understand and improve things. -- Regards, Laurent Pinchart
