On Fri, Jul 6, 2018 at 4:36 PM Lukas Wunner <lukas@xxxxxxxxx> wrote: > > [cc += Kishon Vijay Abraham] > > On Thu, Jul 05, 2018 at 11:18:28AM +0200, Rafael J. Wysocki wrote: > > OK, so calling devices_kset_move_last() from really_probe() clearly is > > a mistake. > > > > I'm not really sure what the intention of it was as the changelog of > > commit 52cdbdd49853d doesn't really explain that (why would it be > > insufficient without that change?) > > It seems 52cdbdd49853d fixed an issue with boards which have an MMC > whose reset pin needs to be driven high on shutdown, lest the MMC > won't be found on the next boot. > > The boards' devicetrees use a kludge wherein the reset pin is modelled > as a regulator. The regulator is enabled when the MMC probes and > disabled on driver unbind and shutdown. As a result, the pin is driven > low on shutdown and the MMC is not found on the next boot. > > To fix this, another kludge was invented wherein the GPIO expander > driving the reset pin unconditionally drives all its pins high on > shutdown, see pcf857x_shutdown() in drivers/gpio/gpio-pcf857x.c > (commit adc284755055, "gpio: pcf857x: restore the initial line state > of all pcf lines"). > > For this kludge to work, the GPIO expander's ->shutdown hook needs to > be executed after the MMC expander's ->shutdown hook. > > Commit 52cdbdd49853d achieved that by reordering devices_kset according > to the probe order. Apparently the MMC probes after the GPIO expander, > possibly because it returns -EPROBE_DEFER if the vmmc regulator isn't > available yet, see mmc_regulator_get_supply(). > > Note, I'm just piecing the information together from git history, > I'm not responsible for these kludges. (I'm innocent!) > Thanks for your exploration, very clearly. I had tried, but failed since these commits are contributed with different authors. I am not familiar with ARM and dts, so had thought really_probe()->devices_kset_move_last() is used to address a very popular "supplier<-consumer" order issue in smart phone, based on the configuration hard-coded in "bios(or counterpart in ARM). > @Pingfan Liu, if you just remove the call to devices_kset_move_last() > from really_probe(), does the issue go away? > Yes, it goes away. > If so, it might be best to remove that call and model the dependency > with a call to device_link_add() in mmc_regulator_get_supply(). > Another idea would be to automatically add a device_link in the > driver core if -EPROBE_DEFER is returned. > Maybe the first one is better, as it is already used by other drivers. Thanks, Pingfan
