On Tue, Dec 02, 2014 at 09:21:51AM +0000, Frank Binns wrote: > On 01/12/14 15:28, Daniel Vetter wrote: > > On Mon, Dec 01, 2014 at 10:01:37AM +0000, Frank Binns wrote: > >> Hi, > >> > >> We are currently in negotiations with one of our customers (Mediatek) on > >> a strategy that will allow them to push a DRM modesetting driver into > >> the upstream kernel. We are writing to get people's opinions and > >> feedback on our proposed approach. > >> > >> Currently, our driver is structured in such a way that the display > >> driver is more tightly integrated with the GPU driver than we would > >> like. Although our kernel driver has been shipped with a GPL license for > >> a long time, it is not in a form that would be considered acceptable > >> upstream. Unfortunately, it is going to be a long process to get this > >> part of the driver into a reasonable state. However, in the meantime, we > >> don't want to prevent customer portions of the driver from being > >> upstreamed. With the work done on recent kernels, and with a willing > >> partner in Mediatek, we now think that we can restructure our driver in > >> such a way as to allow this to happen. > >> > >> We see two basic approaches to achieving this: > >> 1) Two independent DRM drivers, i.e. modesetting and render node drivers > >> 2) A single componentised DRM driver > >> > >> Our (IMG's) preferred approach is to have a single componentised DRM > >> driver. This is due to the following reasons: > >> > >> - Existing user space is not fully prepared to handle render nodes. > >> > >> - There is concern that any IMG DRM render node driver will need > >> knowledge about multiple SoCs, each one being from a different vendor. > >> Would this be deemed acceptable? > >> > >> - There is a trend, at least for DRM SoC drivers, towards using the > >> component interface. Although there appears to be very few (one?) > >> examples of GPU component drivers. > >> > >> To give some high level details on how we expect the componentised DRM > >> driver model to work, each vendor (in this case Mediatek) will write > >> their own DRM driver (supporting modesetting, dumb buffers, GEM, prime, > >> etc) and IMG will provide an almost entirely independent component > >> driver that adds in GPU support. Until our GPU driver is in a suitable > >> state this will most likely necessitate a small kernel patch to wire up > >> support, e.g. GPU specific ioctls. > >> > >> Cross-device and cross-process memory allocations will be made using the > >> DRM driver. In order for this memory to be shared with the GPU component > >> driver it will be necessary, at least for the time being, to export it > >> via prime and import it via a GPU ioctl. Synchronisation between the > >> display and GPU will be performed via reservation objects. > >> > >> Does this sound like a sane approach? Questions and/or feedback is very > >> welcome. > > Rule of thumb is that if it's an externally licensed IP block it should be > > a separate driver. Which is the case here. The idea is that the mostly > > generic IMG driver could be reused on other platforms that ship the same > > IP-block, while linking up with the respective display controller driver. > > The end result is 2 drm drivers: > > - Display block drm driver which expose KMS objects for modesetting, but > > only very basic gem (just enough to allocate dumb framebuffers and > > import/export dma-bufs). > > - Full-blown gem driver for the img render IP block. > > > > For an example look at the tegra/nouveau combo which can run on TK1. > > > > Plugggin in an IMG driver into each display block like it's currently done > > with all the armsoc stuff on android is imo completely no-go. > > > > Note that the component interface is completely irrelevant wrt the > > interface you expose to userspace. It's just an driver-internal helper > > library useful in certain situation. Not even the drm core really cares > > whether you use component helpers or not. > > > > Thanks, Daniel > > OK, so it seems the consensus is that IMG should provide a separate > render-node only DRM driver. > > Having not worked directly on the core DRM code I'm not completely > familiar with it but it seems to me that the DRIVER_MODESET flag has a > dual meaning. Firstly it means that the driver supports KMS and secondly > it means that a lot of the legacy stuff isn't supported. It also changes > the way in which driver initialisation is performed. Would it make sense > for the DRIVER_RENDER flag to have a similar effect? In other words, > should it turn off legacy stuff and use the newer method of driver > initialisation? DRIVER_MODESET means you have a modern driver which binds to the device. We should probably RENAME it to DRIVER_LEGACY and invert it's sense, but no one has stepped up to the taks. DRIVER_RENDER just means you support render nodes. And new drm driver which exposes driver-specific ioctls should set this flag. Again we should probably rename this to DRIVER_IOCTLS_BROKEN_CANT_DO_RENDER and invert the sense ;-) Ofc with a better neame. So for the IMG render-only driver you'd need to set both. Both flags just hide legacy behaviour if not set, but that's the way you need to do it without changing every driver. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
