On 06/03/2019 03:41, Laurent Pinchart wrote: > Hi Tomi, > > On Fri, Jan 18, 2019 at 10:29:33AM +0200, Tomi Valkeinen wrote: >> On 18/01/19 00:04, Rob Herring wrote: >> >>> Mesa/libdrm already has lots of code to open the correct devices and >>> not care about minor numbers. What's the problem here? >> >> Well, maybe the problem is that I don't know how to do this =). >> >> So, if we have multiple DRM devices, how does one manage those? >> Iterating over them and looking for kms-capable ones is easy enough. But >> if there are multiple kms-capable ones, how should the userspace choose >> between those? >> >> I see that udev creates /dev/dri/by-path/ links to the cards, should the >> userspace use those to have a persistent link to the card? E.g. first >> time the app is ran, it'll collect all the kms-capable cards, and store >> the by-path names somewhere, and in subsequent runs it will instead use >> the by-path names to keep the order the same. >> >> If I have a product with two display controllers, and one of them has >> the main display connected, how does my custom app know which card to >> use? Hardcoding the by-path in the app? > > I think it depends on how you define "main display". We have a similar > problem with cameras where a system such as a phone or tablet with a > front camera and a back camera has no good way to convey the role of > each camera all the way to applications. The information belongs to > system firmware in my opinion (and thus DT in this case), but probably > not in the form of aliases. It would make sense to tag connector and > panels with some kind of role (such as main display, various kind of > auxiliary displays, ...), parse that information in drivers, and report > it to userspace (ideally through standard APIs). I agree. I did have "label" in the omapdrm-style panels and connectors, but that's not used anywhere. But this patch is not really about what you describe above, The target was really just to have card0 to be a modesetting card, making simple apps that use card0 for display working. So, obviously a work-around or even a hack, but solves the issue without changing the userspace. Tomi -- Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
