Date: Sun, 23 Aug 2015 00:09:25 +0000 From: Brian Fundakowski Feldman <brianfundakowskifeldman@gmail.com> To: Adrian Chadd <adrian.chadd@gmail.com> Cc: Tom Jones <jones@sdf.org>, 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%2BOUycUtCiQ9ZVxZjwAkvW0JiGi26tDKpvzD12P1wyEkeQw@mail.gmail.com> In-Reply-To: <CAJ-Vmom4qgXYL5eMPsnprvO4X7CES5ipAc0Z%2BsZtmMmF9K4Fqg@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>
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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" >
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