Date: Fri, 1 Apr 2016 14:12:08 -0700 From: Adrian Chadd <adrian.chadd@gmail.com> To: Brian Fundakowski Feldman <brianfundakowskifeldman@gmail.com> Cc: Warner Losh <imp@bsdimp.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: <CAJ-Vmo=raONYKNuixppFucP79KjuiL3ecmf8atuajKd=BfXdAg@mail.gmail.com> In-Reply-To: <CAEv1%2BOVvdEMx=pWX%2BaZ=PXb-tL=Ce1mZfP0CvXOnKTGTcYPTiA@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> <CAEv1%2BOVvdEMx=pWX%2BaZ=PXb-tL=Ce1mZfP0CvXOnKTGTcYPTiA@mail.gmail.com>
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hihi! ok, I'd now like to resurrect this - I'll take a look and see what's missing before we throw it into the tree. I'd like to use this for the atheros MIPS SPI stuff so i can more efficiently speak to an LCD. :P Thanks! -adrian On 22 August 2015 at 17:27, Brian Fundakowski Feldman <brianfundakowskifeldman@gmail.com> wrote: > 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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