Tomas Carnecky wrote:
The dri/drm interface seems to be quite low-level. I heard somewhere that different devices have quite different registers and work in a quite different way. If it is true that it would be better to make a more high-level interface where every driver can do it's stuff as it needs. How much low/high-level should the interface be so you get the best performance out of these many different devices and don't have to make workarounds in the drivers. I have the impression that the newest cards have quite high-level chips interfaces (supporting shaders etc.).
The design priciple of the open-source drivers is that the kernel part acts as nothing more than a conduit to shove bits into the chip. Because of that, the interface is pretty raw and varies from chip to chip. For DMA programmed chips, the user-mode driver works by filling buffers with "stuff" and asking the kernel to kick of a DMA operation with the buffer. That's why so much of the ioctl inferface is device-dependent. This doesn't make for "workarounds in the drivers", it just means that the user-mode is written to work with its own low-level kernel-mode interface.
On advantage of this is that we don't have to modify the kernel drivers very often. Some of the drivers have had regular updates to the user-mode part, but thier kernel driver hasn't been modified in over a year. For us, that's a *big* advantage.
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