On Mon, Jun 29, 2015 at 2:06 PM, Mario Kleiner <[email protected]> wrote:
> > The bits are not a bit mask where a specific bit position corresponds to a > specific pipe, but those bits encode a 5 bits wide pipe number between 0 > and (2^5)-1 ie. 0-31. The comment in the code snippet you show about bits > 1-6 is a bit inaccurate, as it is only bits 1-5, looking at the > DRM_VBLANK_HIGH_CRTC_MASK. > > You could address output->pipe 0 and 1 also with that code. The reason for > the special case of pipe 0 and 1 is backwards compatibility with older > kernels which didn't support passing in a pipe number, but instead had "no > special flags" for pipe 0 and the DRM_VBLANK_SECONDARY flag for pipe 1. A > leftover from the days when there were only single/dual-head graphis cards. > > But apart from that this is just code transplanted from the x-org video > drivers which i tested at some point both on NVidia quad-head (nouveau) and > AMD six-head gpu's (radeon). > Thank you. I can see now that this is a "request" being constructed and thus it only has to describe one crtc at a time. I was picturing a word of flags returned from the card that was being masked against and could not see how using the number as a mask would make any sense.
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