Date: Sat, 22 Aug 2020 00:59:25 +0400 From: Alexander Mishin <mishin@mh.net.ru> To: freebsd-arm@freebsd.org Subject: Re: Kmod driver at iicbus. attach() and config_intrhook(9) Message-ID: <496ed13afb2327d6416664b4dacfc346@mh.net.ru> In-Reply-To: <d709ba1d3473f5d4353dc1109c198f8acb8ffa28.camel@freebsd.org> 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>
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Ian Lepore писал 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
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