On Tue, 2 Nov 2021 at 03:16, ChiaWei Wang <chiawei_wang@xxxxxxxxxxxxxx> wrote: > > Hi Jae, > > > From: linux-arm-kernel <linux-arm-kernel-bounces@xxxxxxxxxxxxxxxxxxx> On > > > > From: Jae Hyun Yoo <jae.hyun.yoo@xxxxxxxxxxxxxxx> > > > > If LPC KCS driver is registered ahead of lpc-ctrl module, LPC KCS block will be > > enabled without heart beating of LCLK until lpc-ctrl enables the LCLK. This > > issue causes improper handling on host interrupts when the host sends > > interrupts in that time frame. > > Then kernel eventually forcibly disables the interrupt with dumping stack and > > printing a 'nobody cared this irq' message out. > > > > To prevent this issue, all LPC sub drivers should enable LCLK individually so this > > patch adds clock control logic into the LPC KCS driver. > > Have all LPC sub drivers could result in entire LPC block down if any of them disables the clock (e.g. driver unload). > The LPC devices such as SIO can be used before kernel booting, even without any BMC firmware. > Thereby, we recommend to make LCLK critical or guarded by protected clock instead of having all LPC sub drivers hold the LCLK control. > > The previous discussion for your reference: > https://lkml.org/lkml/2020/9/28/153 Please read the entire thread. The conclusion: https://lore.kernel.org/all/CACPK8XdBmkhZ8mcSFmDAFV8k7Qj7ajBL8TVKfK8c+5aneUMHZw@xxxxxxxxxxxxxx/ That is, for the devices that have a driver loaded can enable the clock. When they are unloaded, they will reduce the reference count until the last driver is unloaded. eg: https://elixir.bootlin.com/linux/latest/source/drivers/clk/clk.c#L945 There was another fork to the thread, where we suggested that a protected clocks binding could be added: https://lore.kernel.org/all/160269577311.884498.8429245140509326318@xxxxxxxxxxxxxxxxxxxxxxxxxx/ If you wish to use this mechanism for eg. SIO clocks, then I encourage Aspeed to submit a patch to do that. Cheers, Joel
