Re: Kmod driver at iicbus. attach() and config_intrhook(9)

Ian Lepore писал 2020-08-19 19:39:
> On Wed, 2020-08-19 at 00:24 -0700, Oleksandr Tymoshenko wrote:
>> Andriy Gapon ([email protected]) wrote:
>> > On 18/08/2020 22:05, Alexander Mishin wrote:
>> > > Hi
>> > > ...
>> > > But I see that some other devices (from /usr/src/sys/dev) uses
>> > > CONFIG_INTRHOOK(9)
>> > > on attach() for initialize themselfs.
>> > > I wonder if I need this too? ...
>> >
>> > This is usually needed when a driver needs to talk to its device
>> > while
>> > attaching.  E.g., to set some initial configuration or to confirm
>> > device's
>> > identity, etc.
>> 
>> To extend Andriy's explanation a bit: all these operations may
>> perform
>> I2C transfers and most I2C controllers use interrupts to get notified
>> about tranfer status change (finished, error, etc...). There is no
>> guarantee that when driver's attach method is called interrupts are
>> globally enabled. What would happen in this case is: I2C controller
>> is going to initiate I2C operation and wait for an interrupt that's
>> never going to be delivered. CONFIG_INTRHOOK is a solution for this
>> problem, if your attach method requires interrupts - just split it
>> in two parts and postpone running interrupt-dependent part until
>> after
>> interrupts are globally enabled.
>> 
> 
> A note about all this:  It should never be necessary for an i2c slave
> device driver to do this.  The reason it's needed is because many i2c
> controller drivers attach the iicbus from their attach() routine even
> though they can't actually do i2c IO until interrupts are available.
> It is these controller drivers that should have the intrhook logic to
> not call bus_generic_attach() until interrupts are available if they
> can't do IO until interrupts are available.
> 
> It has long been my goal to fix all our i2c controller drivers to
> behave correctly, so that i2c slave device drivers don't all need the
> intrhook logic.  But somehow I never get around to it.
> 
> -- Ian

I think, it would be helpful, as it would be possible to return an error 
on early stage, from attach(), if there is no connection with the 
configured device.
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