Date: Thu, 21 Feb 2013 16:02:54 -0700 From: Warner Losh <imp@bsdimp.com> To: Aleksandr Rybalko <ray@freebsd.org> Cc: freebsd-arm@FreeBSD.org, Bernd Walter <ticso@cicely7.cicely.de>, ticso@cicely.de, Ian Lepore <ian@FreeBSD.org>, freebsd-mips@FreeBSD.org Subject: Re: SPI, _sz fields in struct spi_command Message-ID: <ABA2B88F-6450-46E7-B134-CB8AE28265B3@bsdimp.com> In-Reply-To: <20130222005926.2aa6db7f.ray@freebsd.org> References: <20130220142140.f8e5a616c75d72e2519dbc69@freebsd.org> <54C08D8E-4C5F-49AF-BEE6-D78EC05D2A24@bsdimp.com> <CAD44qMXkFH9iR=ym1XBtD88HRadpGkO=WRYvz5xhAVucEuoLEA@mail.gmail.com> <20130220174449.GB6976@cicely7.cicely.de> <CAD44qMXsdrhuNRbpA1a9ikj4BGffVfhv1WY6hsqCxHwVzQAdsg@mail.gmail.com> <20130221022655.6f693eb6.ray@freebsd.org> <20130221014433.GA12189@cicely7.cicely.de> <20130221163026.dbeb03f9c38de3d24a7ab30f@freebsd.org> <CAD44qMU6-GUDy%2BTUJ1Ndtcy7S42BCeSsFis0dMtj9LDOeDLwGA@mail.gmail.com> <20130221163003.GC12189@cicely7.cicely.de> <20130222000207.d1478231.ray@freebsd.org> <1361486385.1185.38.camel@revolution.hippie.lan> <20130222005926.2aa6db7f.ray@freebsd.org>
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On Feb 21, 2013, at 3:59 PM, Aleksandr Rybalko wrote: > On Thu, 21 Feb 2013 15:39:45 -0700 > Ian Lepore <ian@FreeBSD.org> wrote: > >> On Fri, 2013-02-22 at 00:02 +0200, Aleksandr Rybalko wrote: >>> On Thu, 21 Feb 2013 17:30:03 +0100 >>> Bernd Walter <ticso@cicely7.cicely.de> wrote: >>> >>>> On Thu, Feb 21, 2013 at 10:21:00AM -0500, Patrick Kelsey wrote: >>>>>> On Thu, Feb 21, 2013 at 9:30 AM, Aleksandr Rybalko >>>>>> <ray@freebsd.org> wrote: >>>>>>> On Thu, 21 Feb 2013 02:44:33 +0100 >>>>>>> Bernd Walter <ticso@cicely7.cicely.de> wrote: >>>>>>> >>>>>>> On Thu, Feb 21, 2013 at 02:26:55AM +0200, Aleksandr Rybalko >>>>>>> wrote: >>>>>>>> 2. teach consumers to give only correct numbers (very nice >>>>>>>> we have only two SPI devices in tree) >>>>>>>> >>>>>>>> After that we will be able to make drivers for some >>>>>>>> (potential) devices which will require bidirectional >>>>>>>> communication. And controllers which can't do that, will >>>>>>>> just report error in that. I believe peoples thinks before >>>>>>>> attach such devices to controllers, so we will not have >>>>>>>> such incompatibility. >>>>>>> >>>>>>> I don't think there are many devices requiring RX/TX at the >>>>>>> same time. >>>>>> >>>>>> Anyway, we will be able to do that, and we don't care now >>>>>> because don't have such drivers yet. >>>>>> >>>>> >>>>> Taking the view that "RX/TX at the same time" means that one >>>>> wants to send meaningful data to the slave device at the same >>>>> time one is interested in what data is returned during that >>>>> transmission, there are such devices in use out there. Linear >>>>> Technologies has several ADCs, such as the LTC2446, for which >>>>> you obtain the previous conversion result while sending the >>>>> configuration bits for the next conversion to be performed. >>>> >>>> Forgot about ADC with channel selection. >>>> >>>>> Although this is slightly out of focus for the specific issue >>>>> originally raised, while on the topic of things that need to get >>>>> done on SPI in real systems, there are also devices out there >>>>> that require specific data or some number of clocks to be >>>>> provided while chip select is deasserted. One example of the >>>>> former is the LTC2404, which is a multichannel ADC for which >>>>> the input channel for the next conversion is selected by the >>>>> last four bits clocked in *before* chip select is asserted. >>>>> One example of the latter is the spec for SPI access to MMC/SD >>>>> cards, which requires a certain number of clocks to be applied >>>>> with chip select deasserted in order to initialize the card. >>>>> If you ever find yourself wondering why an SPI software >>>>> interface provides independent bus acquisition and chip select >>>>> control, the reason is to support these types of devices. >>>> >>>> With many ADC you also want probing support. >>>> Assign CS and GPIO-read MISO for ready without clocking. >>>> Some flash chips also work this way. >>>> Not sure if AT45DB support this and how our driver works. >>>> With own projects I usually ask AT45DB about ready state by >>>> transfering a status word. >>>> >>>> -- >>>> B.Walter <bernd@bwct.de> http://www.bwct.de >>>> Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner >>>> uvm. >>> >>> Guys, I don't said it will not be supported. :) >>> I said drivers of controllers who can't will return error in that >>> case, but other might be ok. >>> >>> So, conclusion: go-go-go ray! do it please! >>> :-D >>> >> >> One other little thought to consider... since tx and rx size must be >> the same if they're both non-zero, then could we change to having a >> single io_size field, and pass a NULL pointer for rx or tx buffer if >> that part of the transfer isn't needed? >> >> -- Ian >> >> > > Yeah, very-very good idea! That how my uncommited driver for i.MX515 > SPI works :) > > Objections? I'm cool with that. Warner
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