Sven Luther wrote: > On Wed, May 28, 2008 at 08:07:10PM +0200, Denis Oliver Kropp wrote: >> Brian G. Rhodes wrote: >> I don't think a new kernel graphics interface should be added, instead using >> UIO to access MMIO, DMA and IRQs would be enough and implement most of the >> graphics driver in user space. Downside is to loose the kernel console which >> you usually don't need on an embedded device... >> >> For acceleration and DMA/IRQ based programming, I still need to check if a >> user space approach would be enough. So far I always handled IRQs in kernel >> space for timing/performance reasons... > > Euh, well, i think the X / OpenGL approach showed us that to do DMA/IRQ, > you need a kernel module, and what X/OpenGL is the DRI thingy.
In some cases performance might be sufficient if IRQs are just routed to user space and handled in a real time thread. You can program the DMA engine from user space, it's just the IRQ that's only arriving in kernel space. > Would it make sense for directfb to re-use this selfsame infrasturcture, > which already exists in the kernel, and is used by X, so kind of > guaranteed to be available for many graphic cards ? If there are drivers within this framework that we could use it makes sense, but for writing support for a new chip one has to consider the overhead of using a framework vs benefits. Overhead could be in time to develop and/or at runtime. Benefits could be safety by relying on proven core code, but also saving time to develop by having to write less code. > But maybe it is too complex or something ? It depends on what you need in kernel space. Have a look at the SH7722 kernel module. I'm not sure if the benefits of DRI would be that big to compensate for the overhead or limitations. E.g. this driver manages a self running DMA queue, where in the ideal case you never have to do any system call, but just append data to the DMA buffer from user space. http://git.directfb.org/?p=core/DirectFB.git;a=blob;f=gfxdrivers/sh7722/kernel-module/sh7722gfx.c This driver handles different interrupt sources, provides DMA for the accelerator as mentioned above and implements a minor portion of JPEG encoding and decoding with the rest done in user space. -- Best regards, Denis Oliver Kropp .------------------------------------------. | DirectFB - Hardware accelerated graphics | | http://www.directfb.org/ | "------------------------------------------" _______________________________________________ directfb-users mailing list directfb-users@directfb.org http://mail.directfb.org/cgi-bin/mailman/listinfo/directfb-users
