On Tue, Dec 02, 2014 at 04:10:15PM +0100, Daniel Vetter wrote: > 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.
Actually I did[0] a while ago. This is the second time that this has come up within a month, so perhaps I should revive the series. Thierry [0]: http://lwn.net/Articles/588016/ -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 836 bytes Desc: not available URL: <http://lists.freedesktop.org/archives/dri-devel/attachments/20141202/a500631b/attachment.sig>
