Messages in this thread | | | Subject | Re: [PATCH v3] driver core: Break infinite loop when deferred probe can't be satisfied | From | Grant Likely <> | Date | Thu, 26 Mar 2020 15:20:27 +0000 |
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On 26/03/2020 15:01, Grant Likely wrote: > > > On 25/03/2020 12:51, Andy Shevchenko wrote: >> On Tue, Mar 24, 2020 at 08:29:01PM -0700, Saravana Kannan wrote: >>> On Tue, Mar 24, 2020 at 5:38 AM Andy Shevchenko >>> <andriy.shevchenko@linux.intel.com> wrote: [...] >>>> ...but extcon driver is still missing... >>>> >>>> [ 22.283174] platform dwc3.0.auto: Added to deferred list >>>> [ 22.288513] platform dwc3.0.auto: >>>> driver_deferred_probe_add_trigger local counter: 1 new counter 2 >>> >>> I'm not fully aware of all the USB implications, but if extcon is >>> needed, why can't that check be done before we add and probe the ulpi >>> device? That'll avoid this whole "fake" probing and avoid the counter >>> increase. And avoid the need for this patch that's touching the code >>> code that's already a bit delicate. >> >>> Also, with my limited experience with all the possible drivers in the >>> kernel, it's weird that the ulpi device is added and probed before we >>> make sure the parent device (dwc3.0.auto) can actually probe >>> successfully. >> >> As I said above the deferred probe trigger has flaw on its own. >> Even if we fix for USB case, there is (and probably will be) others. > > Right here is the driver design bug. A driver's probe() hook should > *not* return -EPROBE_DEFER after already creating child devices which > may have already been probed. > > It can be solved by refactoring the driver probe routine. If a resource > is required to be present, then check that it is available early; before > registering child devices.
If it is difficult to determine whether extcon is available before creating the child devices, then there is a way to solve it that still leverages the driver core. You could refactor dwc3_core_init_mode() into a set of separate probe() routines, one for each mode. dwc3_probe() could register the matching child device just before it exits. Then the driver core will take care of calling it again at a later point in time without tearing down the ulpi device probe.
Cheers, g.
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