Date: Thu, 03 Sep 2020 08:48:18 -0600 From: Ian Lepore <ian@freebsd.org> To: Alexander Mishin <mishin@mh.net.ru>, freebsd-arm@freebsd.org Subject: Re: Re: Re: Re: Re: Kmod driver at iicbus. attach() and config_intrhook(9) Message-ID: <739e424429ecde302e11df4c183d4e62c263a6d6.camel@freebsd.org> In-Reply-To: <8c4593191cccecfe6927c6628e62c742@mh.net.ru> References: <0496ebc5628a015c005c150549e1e70a@mh.net.ru> <20200901221839.GY4213@funkthat.com> <7498213a-28d8-f20c-35ae-97aaf2796c1e@FreeBSD.org> <8c4593191cccecfe6927c6628e62c742@mh.net.ru>
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On Thu, 2020-09-03 at 15:02 +0400, Alexander Mishin wrote: > Andriy Gapon ΠΙΣΑΜ 2020-09-03 11:29: > > On 02/09/2020 01:18, John-Mark Gurney wrote: > > > So my reading of the twsi driver is that it handles things correctly > > > allowing devices pre-interrupts to attach, and using interrupts for > > > transfers post-cold. > > > > I just want to note that twsi uses _completely_ different code for > > polled and > > interrupt modes. So, while either mode should be active at correct > > times, I > > cannot certify that the polled mode works correctly for all transfer > > types. > > I haven't reviewed the polled mode code. > > This adds some more light on my question. > > As a result: > For twsi I use iicbb_transfer() (as Emmanuel Vadot recommended to > someone on the mailing list). > It is definitely not works for my driver, until interrupts went enabled. > But it works perfectly well with the config_intrhook(). > > I have never tried iicbus_write() at boot time yet, but I think I'll > try, just to know for the future. > > Thanks > iicbb_transfer() is for bit-bang i2c; hopefully that was a typo. All i2c slave drivers should be using iicbus_transfer_excl() or the iicdev_readfrom()/iicdev_writeto() helper functions. The only time to use iicbus_transfer() directly is when you need to conduct a dialog with one or more slaves using multiple transactions and it's important to keep the bus locked across the entire series of transactions for some reason (meaning you must handle the acquire/release bus stuff yourself). There is virtually never a reason to call the low-level start/stop/read/write functions directly. It's a pity that this stuff is so horribly documented. It has evolved extensively over the years, not always in good ways, and documentation and examples either don't exist or haven't kept up. Bottom line: if the twsi driver has the config_intrhook logic in it then your driver shouldn't need it. If you do need it, something is broken, either in your driver or in the twsi driver, and we should figure out what the real problem is. -- Ian
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