Hi Sam, On Sat, Jan 12, 2019 at 9:03 PM Sam Ravnborg <s...@ravnborg.org> wrote: > > Hi Jagan. > > > > But as we just assert reset (set it to 0), this timing constraint can be > > > ignored. > > > > But we unaware of reset pulse duration right? it's the hardware that > > bring the reset assert if we set the line 0. am I correct or do we > > need to explicitly wait 10us after reset initiated? > > there is family of chip Sitronix st7789v which don't taking care of > > this sequence (I don't know why?) in > > drivers/gpu/drm/panel/panel-sitronix-st7789v.c with Page 48 of > > datasheet[2] > > > The prepare sequence used is: > 1) reset > 20 ms > 2) regulator enable > 20 ms > 3) unassert reset > 20 ms > 4) assert reset > 30 ms > 4) unassert reset > 150 ms > 5) SOFT RESET > 5 ms > 6) Exit SLEEP mode > sleep_delay (120 ms) > 7) COMMANDS > > The enable sequence is > 1) Display ON > 2) backlight enable > > > The disable sequence is > 1) backlight disable > 2) Display OFF > > The unprepare sequence is > 1) Exit SLEEP mode <= this should be Enter SLEEP mode (covered by previous > mail) > sleep_delay (120 ms) > 2) assert reset > 3) unassert reset > 4) assert reset > 5) regulator disable > > > The implementation in simple-panel supports a long list of panels so we > can assume this is a good reference implementation. > Unless your combo of st7701 + panel has special requirements. > > Prepare sequence: > ----------------- > - Just set reset to 1 - no need to trigger an edge. > But if you somehow think the edge is required keep the current code > but drop the delays that are not required. > We can assume power is OK when it is enabled, no extra waiting required. > - No reason to unassert and then assert and then unassert reset. > > In other words: > - Delay between 1 and 2 can be dropped. > - step 3 and step 4 can be dropped > > Unprepare sequence: > ------------------- > Enter SLEEP mode may take 120 ms so delay between 1) and 2) is OK. > No reason to do the reset dance, drop 2) and 3) > Make sure reset is completed, so wait before leaving the function. > See note 3. on page 54 in datasheet: > > "During the Resetting period, the display will be blanked > (The display is entering blanking sequence, which maximum > time is 120 ms, when Reset Starts in Sleep Out –mode. > The display remains the blank state in Sleep In –mode.) and > then return to Default condition for Hardware Reset." > > We have already sent an Enter SLEEP command but we have no timing constrains > when panel is in SLEEP mode, So stick to the 120 ms. > Just use sleep_delay.
So we need this delay even after reset unlike SLEEP mode delay. OK, thanks for the points will try to check all these points. When did .unprepare and .disable are actually called? I turn-off the backlight by echo 1 > /sys/class/backlight/backlight/bl_power and even power of the board I assume the video transmission stop so it would ended-up calling these, but I couldn't see prints. does it the same time uart dead or something? do you have any inputs on sanity testing of typical panels, if yes please share. Jagan.
