The SPI bus controlled by the pxa2xx driver is on the LPSS, which, yes, corresponds to the Low Power IO Controller in that block diagram.
On 1/26/15, 10:38 PM, "Kevin Shelton" <[email protected]> wrote: >Thanks John and Darren. I will play with spid_devtest and have >reached out to [email protected]. > >A minnowmax-specific question: In the Baytrail block diagram at >http://media.bestofmicro.com/Y/3/400395/original/bay-trail-soc.jpg >does the Marvell pxa27x correspond to the "Low Power IO Controller"? > >On Mon, Jan 26, 2015 at 6:33 PM, Darren Hart <[email protected]> >wrote: >> On 1/26/15, 5:52 PM, "John Hawley" <[email protected]> wrote: >> >>>On 01/26/2015 05:47 PM, Kevin Shelton wrote: >>>> >>>> >>>> On Fri, Jan 23, 2015 at 2:41 PM, John Hawley <[email protected] >>>> <mailto:[email protected]>> wrote: >>>> >>>> > I saw the thread 'Adding an SPI device to the Minnowboard' from >>>>late >>>> > 2013 and 'SPI support on minnowboard v1' from Aug 2014. >>>> > >>>> > Darren Hart notes: >>>> > Ultimately we want to do things like this without board files by >>>>using >>>> > the _DSD mechanisms introduced by the ACPI 5.1 specification >>>>last >>>>week >>>> > >>>> > I just wanted to confirm the ACPI mechanism is not the >>>>recommended way >>>> > yet, and that using low-speed-spidev.c as a template is still >>>>the >>>>way to go. >>>> >>>> The answer to that will depend on what kernel you are intending to >>>> target. Kernel's with ACPI 5.1 _DSD support, I think you'd want >>>>to >>>>push >>>> on that. Older kernels without that, likely spidev or a more >>>>targeted >>>> driver. >>>> >>>> >>>> Currently, I am targeting 3.17. 3.17 does not have ACPI 5.1 _DSD >>>> support, correct? >>> >>>Off the top of my head that came in in 3.18, so yes that's correct. >> >> 3.19 iirc. >> >> Also, using _DSD required a firmware change, or at least a DSDT update. >> >>> >>>> > Additional q: >>>> > How do you tell the SPI controller that you have an active-high >>>>instead >>>> > of the usual active-low device? Is it correct to do a bitwise >>>>or >>>>with >>>> > SPI_CS_HIGH (0x4) with your SPI_MODE in your spi_board_info >>>>struct, like: >>>> > .mode = SPI_MODE_0 | SPI_CS_HIGH >>>> >>>> That should work, but take my statement with a grain of salt as I >>>> haven't tried it with a device. >>>> >>>> >>>> It seems to have no effect that I can discern. Pin 5 idles at 3.3V >>>> whether I have >>>> .mode = SPI_MODE_3 | SPI_CS_HIGH >>>> -or- >>>> .mode = SPI_MODE_3 >>>> >>>> I threw in a >>>> pr_info("SPI mode=%i\n", cod_spi_board_info.mode); >>>> to sanity check that I am setting the mode to what I think I am (3 or >>>>7). >>>> >>>> Any debugging ideas? >>>> What is the best way to learn more about the SPI master? It's built >>>> into the CPU, correct? >>>> This smells in the ballpark of >>>> relatedness: >>>>http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/263467. >>>>ht >>>>ml >>>> I don't grok that patch, but I confirmed my version of pxa2xx.c in my >>>> 3.17 tree appears to contain that change. >>> >>>The SPI interface is indeed built into the CPU. It's the pxa2xx core, >>>which it looks like you've found. I'd have to punt to someone else, as >>>I'll admit, I don't know the SPI code well enough to say what's going >>>on. I've CC'ed Darren Hart, he might know who to check with next. >> >> Those are some very specific SPI usage questions that I don't know the >> answer to off the top of my head. To find out, I would: >> >> 1) Search for other drivers in tree and externally that use active-high >> >> First hit looks interesting: >> https://www.kernel.org/doc/Documentation/spi/spidev_test.c >> >> >> 2) Lookup the right mailing lists for SPI Linux kernel development and >>ask >> the same question there >> >> -- >> Darren Hart >> Intel Open Source Technology Center >> >> >> >> _______________________________________________ >> elinux-MinnowBoard mailing list >> [email protected] >> http://lists.elinux.org/mailman/listinfo/elinux-minnowboard > -- Darren Hart Intel Open Source Technology Center _______________________________________________ elinux-MinnowBoard mailing list [email protected] http://lists.elinux.org/mailman/listinfo/elinux-minnowboard
