Date: Thu, 21 Feb 2013 15:39:45 -0700 From: Ian Lepore <ian@FreeBSD.org> To: Aleksandr Rybalko <ray@FreeBSD.org> Cc: freebsd-arm@FreeBSD.org, Bernd Walter <ticso@cicely7.cicely.de>, ticso@cicely.de, freebsd-mips@FreeBSD.org Subject: Re: SPI, _sz fields in struct spi_command Message-ID: <1361486385.1185.38.camel@revolution.hippie.lan> In-Reply-To: <20130222000207.d1478231.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>
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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
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