Date: Sun, 23 Aug 2015 00:27:50 +0000 From: Brian Fundakowski Feldman <brianfundakowskifeldman@gmail.com> To: Warner Losh <imp@bsdimp.com> Cc: Adrian Chadd <adrian.chadd@gmail.com>, Luiz Otavio O Souza <loos@freebsd.org>, "freebsd-embedded@freebsd.org" <embedded@freebsd.org> Subject: Re: spigen(4) SPI Generic IO interface -- need comments Message-ID: <CAEv1%2BOVvdEMx=pWX%2BaZ=PXb-tL=Ce1mZfP0CvXOnKTGTcYPTiA@mail.gmail.com> In-Reply-To: <CANCZdfo%2Bd2oA86iw_OXLros%2BBnVQZZqt2D_rWQMp-R6FNH5ueQ@mail.gmail.com> References: <CAEv1%2BOU4cFpMpeQGfnCP7L4Q_k18rOSOA9JBnKUa99DS5dFnWA@mail.gmail.com> <20150817160423.GB3078@gmail.com> <CAEv1%2BOUhSAJxxWAfW2GUFVw=H-_KOs2dGg2d7uhZnFbqsHE5Qw@mail.gmail.com> <CAEv1%2BOXe4w8hJXQu2MsoMLz6ixeG3hU3BmLZpssG15SaPd9JGw@mail.gmail.com> <CAJ-Vmom4qgXYL5eMPsnprvO4X7CES5ipAc0Z%2BsZtmMmF9K4Fqg@mail.gmail.com> <CAEv1%2BOUycUtCiQ9ZVxZjwAkvW0JiGi26tDKpvzD12P1wyEkeQw@mail.gmail.com> <CANCZdfo%2Bd2oA86iw_OXLros%2BBnVQZZqt2D_rWQMp-R6FNH5ueQ@mail.gmail.com>
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You know, now you're making me wonder if the edge behavior shouldn't also be configurable per-spigen/per-transfer. Chip select polarity seems far too dangerous to expose that way. The only SPI device I have lying around so far is an MCP3008. On Sat, Aug 22, 2015, 8:17 PM Warner Losh <imp@bsdimp.com> wrote: > I've worked on one set of flash that had simple commands for identifying > it, which were clocked at one rate (slow, to be compatible with older > members of the family), and other commands that were data transfer that > were clocked faster to match the data coming from internal pipelines in the > part. I don't know how common this arrangement is in the wild, though. > > And all of this is from memory of something I worked on maybe 10 years ago > now, so I'm not sure how relevant it is today. I do know NAND flash chips > have similar behavior, but those don't have a SPI bus. > > Warner > > > On Sat, Aug 22, 2015 at 6:09 PM, Brian Fundakowski Feldman < > brianfundakowskifeldman@gmail.com> wrote: > >> That's something I want feedback on: are there scenarios where you want to >> regularly vary the clock to a specific SPI device, as opposed to varying >> it >> among several? It would be easy to add to the transfer ioctls if you have >> a >> use case (for example, manual chip select control with more devices than >> chip select pins in your low-level SPI implementation.) Certainly from a >> runtime cost perspective it would be no burden. >> >> Thanks for taking a look! >> -- >> green >> >> On Sat, Aug 22, 2015, 5:55 PM Adrian Chadd <adrian.chadd@gmail.com> >> wrote: >> >> > Hi! >> > >> > This looks cool! Is there any reason why the clock isn't per >> transaction? >> > >> > >> > -a >> > >> > >> > On 22 August 2015 at 11:23, Brian Fundakowski Feldman >> > <brianfundakowskifeldman@gmail.com> wrote: >> > > I've added a couple more features: >> > > * clock adjustment via ioctl, independent per spigenN device >> > > * mmap(2) support for very low latency >> > > >> > > On Tue, Aug 18, 2015 at 6:47 PM, Brian Fundakowski Feldman < >> > > brianfundakowskifeldman@gmail.com> wrote: >> > > >> > >> On Mon, Aug 17, 2015 at 12:04 PM Tom Jones <jones@sdf.org> wrote: >> > >> >> > >>> On Mon, Aug 17, 2015 at 10:00:26AM -0400, Brian Fundakowski Feldman >> > wrote: >> > >>> > I'm woefully out-of-practice with my kernel hackery (but still >> pretty >> > >>> > proficient in jiggery-pokery) so I would like to get comments on a >> > >>> little >> > >>> > driver I just made for interfacing arbitrarily in userland with >> SPI >> > >>> > components. The only thing I'm exposing is a /dev/spigenN node >> with >> > a >> > >>> > single transfer ioctl and I put together a test circuit and >> program >> > >>> with an >> > >>> > MCP3008 10-bit ADC IC to validate that it basically works, other >> than >> > >>> the >> > >>> > limitation that the transfers must be octet-multiply-sized, but I >> > >>> haven't >> > >>> > looked at the SoC's (I'm using a Raspberry Pi 2) data sheet to >> tell >> > >>> whether >> > >>> > that's just a limit on the spibus(4) interface or the Broadcom SPI >> > >>> driver >> > >>> > or the Broadcom SoC itself. >> > >>> > >> > >>> > I hit one snag in development where I simply called the ioctl >> wrong >> > and >> > >>> > found copyin(9) to page fault HARD if given a bogus user address >> to >> > copy >> > >>> > from, and panic the kernel. I can post up the test program if >> anyone >> > >>> wants >> > >>> > but it's very trivial: I just align the start bit and the command >> > data >> > >>> into >> > >>> > the least significant bits of the first octet, shift it up two >> > >>> positions so >> > >>> > the NULs get clocked out as part of the command field, and provide >> > two >> > >>> > octets for the data field to retrieve back the 10-bit digital >> value. >> > >>> >> > >>> Oh, cool. >> > >>> >> > >>> I did the same earlier this year, have you seen[1]?. >> > >>> >> > >>> The FreeBSD i2c api is the same/very similar the linux one[2][3]. >> Have >> > you >> > >>> considered adding some of the ioctls[3] or the data structures to >> make >> > it >> > >>> easier to port code? >> > >>> >> > >>> [1]: >> > >>> >> > >> https://lists.freebsd.org/pipermail/freebsd-embedded/2015-April/002466.html >> > >>> [2]: https://www.kernel.org/doc/Documentation/i2c/dev-interface >> > >>> [3]: >> > >>> >> > >> https://www.freebsd.org/cgi/man.cgi?query=iic&apropos=0&sektion=0&manpath=FreeBSD+10.2-RELEASE&arch=default&format=html >> > >>> [4]: https://www.kernel.org/doc/Documentation/spi/spidev >> > >> >> > >> >> > >> I've iterated a bit on this to try to make some more sensible API, >> > >> behaving reasonably about being able to set the SPI clock speed. I'm >> > going >> > >> to implement an mmap handler so I can have my low-latency operation >> > mode, >> > >> as well. I don't like the Linux APIs one bit because it's just not >> > safe to >> > >> allow all those configuration changes on a per-transfer basis... >> > >> >> > >> Moving this to -embedded because it's more apt than -hackers. >> > >> >> > > >> > > _______________________________________________ >> > > freebsd-embedded@freebsd.org mailing list >> > > https://lists.freebsd.org/mailman/listinfo/freebsd-embedded >> > > To unsubscribe, send any mail to " >> > freebsd-embedded-unsubscribe@freebsd.org" >> > >> _______________________________________________ >> freebsd-embedded@freebsd.org mailing list >> https://lists.freebsd.org/mailman/listinfo/freebsd-embedded >> To unsubscribe, send any mail to " >> freebsd-embedded-unsubscribe@freebsd.org" >> > >
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