From owner-freebsd-embedded@freebsd.org Sun Aug 23 00:09:36 2015 Return-Path: Delivered-To: freebsd-embedded@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id E94819C0986 for ; Sun, 23 Aug 2015 00:09:35 +0000 (UTC) (envelope-from brianfundakowskifeldman@gmail.com) Received: from mailman.ysv.freebsd.org (mailman.ysv.freebsd.org [IPv6:2001:1900:2254:206a::50:5]) by mx1.freebsd.org (Postfix) with ESMTP id C6777AFB for ; Sun, 23 Aug 2015 00:09:35 +0000 (UTC) (envelope-from brianfundakowskifeldman@gmail.com) Received: by mailman.ysv.freebsd.org (Postfix) id C32859C0985; Sun, 23 Aug 2015 00:09:35 +0000 (UTC) Delivered-To: embedded@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id A7C1B9C0984 for ; Sun, 23 Aug 2015 00:09:35 +0000 (UTC) (envelope-from brianfundakowskifeldman@gmail.com) Received: from mail-ig0-x22f.google.com (mail-ig0-x22f.google.com [IPv6:2607:f8b0:4001:c05::22f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 69941AF9; Sun, 23 Aug 2015 00:09:35 +0000 (UTC) (envelope-from brianfundakowskifeldman@gmail.com) Received: by igui7 with SMTP id i7so35576118igu.0; Sat, 22 Aug 2015 17:09:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-type; bh=Lc4d3tAbZfzj/owXxlxafKmuBA4JdLm2AIzLURifDmU=; b=Tp/Gf55G7wWA4m1T3/xAbeNvdLEIngSNOCj7jgIealowPD00wx0HLvNbsWYoImgrDh 3RYqk1xBwPxWE0Z1Lon+PvxgdubDBaRAqsWP/Kqck7xPCQiHdMg6AK3QVWk1OMx9YObh 8n1bbsC7YkdNhaodgr5NgkI7HKhuxcIJvuVn8vCOc5z9NxkxraFjwlV2CgR4zaB3uNFX JjGZqb3WA1g4X2ud6YcbBDMxmy1Z5RCfFQ31ucmt5DyNBkR2KfcYnGxyu53NVnSw49qC VBqn3u5/5cgsL2cVBcr9NzudqyViukcvL5d3+2bjO0H1mlmtQRdn1kf+RxDHIRInSmgQ ZBLg== X-Received: by 10.50.43.169 with SMTP id x9mr3537402igl.7.1440288574467; Sat, 22 Aug 2015 17:09:34 -0700 (PDT) MIME-Version: 1.0 References: <20150817160423.GB3078@gmail.com> In-Reply-To: From: Brian Fundakowski Feldman Date: Sun, 23 Aug 2015 00:09:25 +0000 Message-ID: Subject: Re: spigen(4) SPI Generic IO interface -- need comments To: Adrian Chadd Cc: Tom Jones , Luiz Otavio O Souza , "freebsd-embedded@freebsd.org" Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.20 X-BeenThere: freebsd-embedded@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Dedicated and Embedded Systems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 23 Aug 2015 00:09:36 -0000 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 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 > 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 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" >