Date: Mon, 17 Aug 2015 17:04:23 +0100 From: Tom Jones <jones@sdf.org> To: Brian Fundakowski Feldman <brianfundakowskifeldman@gmail.com> Cc: hackers@freebsd.org Subject: Re: spigen(4) SPI Generic IO interface -- need comments Message-ID: <20150817160423.GB3078@gmail.com> In-Reply-To: <CAEv1%2BOU4cFpMpeQGfnCP7L4Q_k18rOSOA9JBnKUa99DS5dFnWA@mail.gmail.com> References: <CAEv1%2BOU4cFpMpeQGfnCP7L4Q_k18rOSOA9JBnKUa99DS5dFnWA@mail.gmail.com>
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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 - tj
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