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@@ -0,0 +1,52 @@ +FAQ for xf86-video-armada +========================= + +Q1. Why does xf86-video-armada Etnadrm backend require etna_viv's + (aka libetnaviv) include files? + +A1. xf86-video-armada's etnaviv backend is shared between the libetnaviv + and etnadrm drivers. The structure of these drivers is: + + Xorg -> etnaviv front end -> gpu command stream -> kernel interface + + The front end is common between etnadrm and etnaviv GPU drivers, + and shares datastructures and function names with libetnaviv. This + means that both GPU drivers generate indentical GPU command streams + for the same Xorg operations. + + The only parts that differ between the two backends is the kernel + interface, which is responsible for submitting the command stream to + the kernel, waiting for completion of these streams, and providing + GPU buffer memory management. + + For etnaviv, we use the libetnaviv library, which requires certain + structures to be used not only at the kernel interface level, but + throughout the driver. + + For etnadrm, we use our own kernel interface which is binary + compatible with libetnaviv. Hence, libetnaviv headers are required + when building etnadrm to maintain binary compatibility with + libetnaviv. + + The alternative would be to maintain and build three entirely + separate GPU backends - which is not desirable. Having common code + which generates exactly the same command stream means that when a + bug is found, we can compare the behaviour of the DRM kernel + support with Vivante's kernel support. + +Q2. Do I need to build etna_viv (aka, libetnaviv) to build the etnadrm + backend? + +A2. No, it should not be necessary to build etna_viv or configure it + when building only the etnadrm GPU backend. xf86-video-armada only + requires the libetnaviv include files in this case. At the time of + writing, these are: + + etnaviv/cmdstream.xml.h + etnaviv/common.xml.h + etnaviv/etna.h + etnaviv/etna_bo.h + etnaviv/etna_util.h + etnaviv/state.xml.h + etnaviv/state_2d.xml.h + etnaviv/viv.h |