* Matthijs van Duin <matthijsvanduin@xxxxxxxxx> [200106 10:07]: > On Sun, Jan 05, 2020 at 12:37:04PM -0800, Tony Lindgren wrote: > > 4. The issue I'm seeing with stellarium on droid4 may be a stride > > issue as about one out of 3 or 4 frames is OK and aligning to > > 512 also fixes the issue maybe because it happens to make > > multiple frames align to 4096 > > Yeah if your buffers are 960 pixels wide (assuming the droid4's screen > is natively portrait) and 32bpp then 512-byte alignment suffices to > automatically make them 4KB alignment. Hmm sounds like I need to retest this. But doesn't 512-byte alignment only make the 960 pixels case 2KB aligned? > The most obvious thing I can think of that could do wrong is that it > might contiguously map the pages that cover each line, which is what > will happen if they use e.g. for_each_sg_page, but subsequently assume > that the stride in sgx virtual memory is ALIGN( width * cpp, PAGE_SIZE ) > without taking the offset of the buffer inside the mapping into account. OK > If each line is at most 4KB (i.e. 1024 pixels @ 32bpp) but each line > straddles an MMU page boundary, then the result would be that the even > lines of the frame are written to the top half of the buffer, causing it > to be scaled to 50% vertically, while the odd lines are "lost" (written > outside the buffer, either to a different buffer or unmapped tiler > memory). This sounds like what you described on irc? Yes this sounds like what I've been seeing. Regards, Tony
