On Wed, May 29, 2019 at 08:23:17AM +0200, Linus Walleij wrote: > On Wed, May 29, 2019 at 3:17 AM Brian Masney <masneyb@xxxxxxxxxxxxx> wrote: > > > It's in low speed mode but its usable. > > How low speed is that? I don't have a number but my test with 4.17 is to run 'cat /etc/passwd > /dev/tty1' over a serial cable. The first 2-3 calls will fill up the screen and the file contents appear to show up on the screen immediately to the human eye. The next time that I run it requires scrolling the entire console and there is a small fraction of a second where I see the entire framebuffer contents scroll up. I don't have a graphics background, but I believe that this is the tearing effect that I'm seeing based on what I've read. I believe that disp-te-gpios can be used to mitigate this tearing effect. I have a few questions about this later once we get the basic display working. > > I assume that it's related to the > > vblank events not working properly? > > They are only waiting for 50 ms before timing out, I raised it > to 100ms in the -next kernel. I'm still suspicious about this > even though I think you said this was not the problem. > > For a command mode panel in LP mode it will nevertheless > be more than 100ms for sure, the update is visible to the > naked eye. > > Raise it to 10000 ms or something and see what happens. > drivers/gpu/drm/drm_atomic_helper.c: > msecs_to_jiffies(50) I previously raised those timeouts as high as 5 seconds and it still has the same issue. Writing to /dev/tty1 can take anywhere between a few seconds to 30 seconds or more. Brian
