Date: Mon, 24 Aug 2020 13:47:08 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: Alexander Mishin <mishin@mh.net.ru> Cc: freebsd-arm@freebsd.org Subject: Re: Kmod driver at iicbus. attach() and config_intrhook(9) Message-ID: <20200824204708.GH4213@funkthat.com> In-Reply-To: <496ed13afb2327d6416664b4dacfc346@mh.net.ru> References: <7fabb65d99aaa74775c1daa91bffb873@mh.net.ru> <3249fa7e-554a-83ef-57b2-7c38aa0b4591@FreeBSD.org> <20200819072409.GA59949@bluezbox.com> <05145b71692af74b103bb226a2e93a15e1e851cb.camel@freebsd.org> <d603cf3b852d5e18fa5faa9066f643a3@mh.net.ru> <20200820223918.GC4213@funkthat.com> <d709ba1d3473f5d4353dc1109c198f8acb8ffa28.camel@freebsd.org> <496ed13afb2327d6416664b4dacfc346@mh.net.ru>
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Alexander Mishin wrote this message on Sat, Aug 22, 2020 at 00:59 +0400:
> Ian Lepore ?????????? 2020-08-21 02:51:
> > On Thu, 2020-08-20 at 15:39 -0700, John-Mark Gurney wrote:
> >> Alexander Mishin wrote this message on Thu, Aug 20, 2020 at 10:07
> >> +0400:
> >> > Ian Lepore ?????????? 2020-08-19 19:39:
> >> > > 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
> >> > > > > > ...
> >> > > > > > 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.
> >> >
> >> > 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.
> >>
> >> Looks like there's a function bus_delayed_attach_children designed
> >> exactly for this:
> >> * Many buses can't run transactions on the bus which children need
> >> to probe and
> >> * attach until after interrupts and/or timers are running. This
> >> function
> >> * delays their attach until interrupts and timers are enabled.
> >>
> >> and it looks like a couple controllers are already using it, imx_i2c
> >> and ti_i2c...
> >>
> >> It looks like maybe a simple replace of bus_generic_attach w/
> >> bus_delayed_attach_children should be enough on those w/
> >> interrupts...
> >>
> >> Is there any argument for doing it for ALL controllers instead of
> >> just
> >> some?
> >>
> >> Poking around some, and it looks like some (one) drivers "pretend" to
> >> use interrupts, but just busy wait instead, e.g. exynos5...
> >>
> >
> > Hmm, yeah, it looks like more has been done along these lines than I
> > remembered. In fact, the work may be done.
> >
> > Some i2c controllers have to work properly before interrupts are
> > available, to control things like PMIC chips that are required very
> > early in device configuration. Typically they have some sort of
> > polling mechanism that's used early, and revert to using interrupts
> > once they're available. The allwinner and rockchip drivers work that
> > way.
> >
> > -- Ian
> Just to dot the i's, my SoC is allwinner (Orange PI PC). And the issue
> at boot time really showed itself up until config_intrhook was used.
> FreeBSD myhost.mh.net.ru 13.0-CURRENT FreeBSD 13.0-CURRENT #3 r364004
What driver is used for i2c on the Orange? I've tried to firgure it
out from dts + source, but it isn't clear.
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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