Date: Wed, 19 Aug 2020 09:39:54 -0600 From: Ian Lepore <ian@freebsd.org> To: Oleksandr Tymoshenko <gonzo@bluezbox.com>, Andriy Gapon <avg@freebsd.org> Cc: freebsd-arm@freebsd.org Subject: Re: Kmod driver at iicbus. attach() and config_intrhook(9) Message-ID: <05145b71692af74b103bb226a2e93a15e1e851cb.camel@freebsd.org> In-Reply-To: <20200819072409.GA59949@bluezbox.com> References: <7fabb65d99aaa74775c1daa91bffb873@mh.net.ru> <3249fa7e-554a-83ef-57b2-7c38aa0b4591@FreeBSD.org> <20200819072409.GA59949@bluezbox.com>
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On Wed, 2020-08-19 at 00:24 -0700, Oleksandr Tymoshenko wrote: > Andriy Gapon (avg@FreeBSD.org) wrote: > > On 18/08/2020 22:05, Alexander Mishin wrote: > > > Hi > > > > > > I write a kmod driver for bh1750 light sensor with iic (almost > > > wrote). > > > As usual, probe(), attach() and detach(). On attach() it runs > > > TIMEOUT_TASK_INIT > > > for periodically write opecode, read result and place it to > > > sysctl dev.bh1750.N > > > variables. It is all. > > > > > > 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? ...or maybe... when I might need it? > > > > 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
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