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This leads >>>>>> to unnecessary delays during resume or power-on when the panel becomes >>>>>> ready earlier than the full timeout. >>>>>> >>>>>> This patch splits the total wait time into two pases >>>>>> - First wait for the typical panel-on time(180ms) >>>>>> - If panel is not ready , continue polling in short 20ms intervals >>>>>> until the maximum timeout (5000ms) is reached >>>>> I'm *very* reluctant to merge any new custom wait hacks. I'm in the >>>>> process of *removing* a plethora of them [1][2][3]. >>>> good riddance >>> Yay! >>> >>>>> I think the question is, should xe_mmio_wait32() (and the i915 >>>>> counterpart) and the intel_de_wait*() functions be migrated to an >>>>> interface similar to read_poll_timeout(), i.e. provide sleep and timeout >>>>> separately, no exponential backoff. And implement the waits using >>>>> read_poll_timeout(), or whatever Ville ends up with [4]. >>>> I saw your patch series and I'm eagerly waiting it to either propagate >>>> it in xe or have someone merge such a patch. I'm not sure about >>>> removing the exponential backoff is a good thing overall, but if it's >>>> needed then it needs to be justified to add a new function to pair with >>>> read_poll_timeout(), not a custom driver function. >>> While I'm negative about the patch at hand, the underlying problem is >>> very real. >>> >>> I think at the very least the exponential sleep backoff needs an upper >>> bound that's relative to the timeout. Maybe 10-25% of timeout? >>> >>> With the example case of 5 second timeout, the exponential backoff >>> starting from 10 us leads to a dozen polls before reaching 100 ms >>> elapsed time, but then polls at approximately 1 s, 2 s, 4 s, and 8 s >>> elapsed time. Longer timeouts are of course rare, but they exhibit >>> increasingly worse behaviour. >>> >>> So if what we're waiting takes 2.1 seconds, the next check will be about >>> 2 seconds later. Similarly, if it takes 4.1 seconds, the next check will >>> be about 4 seconds later, in this case exceeding the timeout by 3 >>> seconds. >>> >>> Anyway, if xe_mmio_wait32() remains as it is, with read_poll_timeout() >>> it's trivial to do the wait in the intel_de_*() macros, in display side, >>> with sleeps and timeouts defined in display. Because for most things the >>> really quick fast polls are useless in display. >>> >> This exponential sleep back-off is causing around 120ms additional >> delay in resume compared to  i915. >> >> how about polling as below , use intel_de_read and read_poll_timeout >> >>     ret = read_poll_timeout(intel_de_read, reg_val, >>                     ((reg_val & mask) == value), >>                     (20 * 1000),                        // poll every 20ms >>                     (PANEL_MAXIMUM_ON_TIME_MS * 1000),  // total >> timeout (us) >>                     true, >>                     display, pp_stat_reg); > This would be a temporary measure pending Ville's work [1], but I'm not > against it. > > Also, needs to happen in wait_panel_status() instead of adding a > separate wait_panel_on_status() function. > > BR, > Jani. > > > [1] https://lore.kernel.org/r/20250702223439.19752-1-ville.syrjala@linux.intel.com Adding this logic in wait_panel_status() is causing ~20ms delay when function called from wait_panel_power_cycle() which expects minimal time. Adding new function avoids this scenario. Regards, Dibin > >> Regards, >> >> Dibin >> >>> BR, >>> Jani. >>>