Date: Fri, 1 Mar 2013 00:48:28 +0200 From: Aleksandr Rybalko <ray@freebsd.org> To: Ian Lepore <ian@FreeBSD.org> Cc: Aleksandr Rybalko <ray@FreeBSD.org>, Bernd Walter <ticso@cicely7.cicely.de>, freebsd-arm@FreeBSD.org, freebsd-mips@FreeBSD.org, ticso@cicely.de Subject: Re: SPI, _sz fields in struct spi_command Message-ID: <20130301004828.e0727064.ray@freebsd.org> In-Reply-To: <1361488675.1185.42.camel@revolution.hippie.lan> 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> <1361488675.1185.42.camel@revolution.hippie.lan>
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On Thu, 21 Feb 2013 16:17:55 -0700 Ian Lepore <ian@FreeBSD.org> wrote: > On Fri, 2013-02-22 at 00:59 +0200, 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? > > > > WBW > > So just to be clear... if a device driver passes a NULL tx pointer to > the controller driver, it's saying "My device doesn't care what it > receives during this transfer." If the device needs zeroes or ones > then the buffer full of them has to be provided, right? > > I'm thinking for the controller that does dma, this simplifies things > down to making a bus_dmamem_alloc() call (which is fast these days > because of the zone allocator) and it doesn't bother to set the > contents of that buffer to anything before starting the dma. > > -- Ian > > Hi hackers! Instead of implementation, new thoughts is coming :) Well, after few days of stabilization of ideas I'm beginning new round of talks. :) So, two days ago we had discussion with Ian on IRC. Things we decide: 1. Don't remove current transfer method 2. Add acquire/release methods 3. Add cs control methods 4. Add new transfer method, it will do only one xfer, and as described previously will have only size/txbuf/rxbuf fields in transfer struct. Tx and/or rx can be NULL, so even clocking without data possible. 5. Update old transfer method(spibus_transfer) to do: * acquire * enable cs * transfer cmd * transfer data * disable cs * release bus 6. Add some method which will expose hw ability (one direction at a time, independent cs control, etc.) 7. Maybe some other special methods (Ian said for SD on spi we need ability to xfer w/o CS asserted) That how I see new xfer structure: struct spi_xfer { size_t size; /* Transfer size (bytes) */ void *tx_buf; /* Buffer with TX data (NULL to not tx) */ void *rx_buf; /* Buffer for RX data (NULL for ignore) */ }; Simple and clear :) WBW -- Aleksandr Rybalko <ray@freebsd.org>
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