Re: [PATCH] Do not disable driver and bus shutdown hook when class shutdown hook is set.

[Jason Gunthorpe]

On Wed, Aug 09, 2017 at 11:34:20PM +0200, Michal Suchanek wrote:
> Disabling the driver hook by setting class hook is totally sound design
> not prone to error as evidenced by the single implementation of the
> class hook.

It was done this was for consistency, if you look at the full code:

                if (dev->class && dev->class->shutdown) {
                        if (initcall_debug)
                                dev_info(dev, "shutdown\n");
                        dev->class->shutdown(dev);
                } else if (dev->bus && dev->bus->shutdown) {
                        if (initcall_debug)
                                dev_info(dev, "shutdown\n");
                        dev->bus->shutdown(dev);
                } else if (dev->driver && dev->driver->shutdown) {
                        if (initcall_debug)
                                dev_info(dev, "shutdown\n");
                        dev->driver->shutdown(dev);
                }

The bus disables the driver callback, on the expectation that the bus
implementation will do it.

Existing bus implementations do properly chain to driver shutdown (eg
look at mmc_bus_shutdown) and it appears to have been written like
this so that the bus can insert code before and after calling the
driver shutdown.

Making class act differently from bus seems very confusing, IHMO,
which why the TPM patch was written to follow the existing pattern.

Jason