[MinnowBoard] SPI questions

Darren Hart dvhart at linux.intel.com
Wed Jan 28 05:21:52 UTC 2015

This changes the mechanism used to enumerate the hardware device to the
OS. Recent Linux kernels 3.16+ support for ACPI and PCI enumeration. ACPI
is supported since 3.14. Either should work for a board-file.


On 1/27/15, 3:13 PM, "Kevin Shelton" <kmshelton at gmail.com> wrote:

>sorry for the not clear writing: I meant to say ACPI mode for the
>"LPSS & SCC Devices Mode" setting
>On Tue, Jan 27, 2015 at 3:11 PM, Kevin Shelton <kmshelton at gmail.com>
>> I realized that in my BIOS settings, I was in ACPI mode.  Do I need to
>> be in PCI mode to use a board file?  What does that ACPI-PCI switch in
>> the BIOS do?  thanks for all the help
>> On Mon, Jan 26, 2015 at 11:35 PM, Darren Hart <dvhart at linux.intel.com>
>>> 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" <kmshelton at gmail.com> wrote:
>>>>Thanks John and Darren.  I will play with spid_devtest and have
>>>>reached out to linux-spi at vger.kernel.org.
>>>>A minnowmax-specific question: In the Baytrail block diagram at
>>>>does the Marvell pxa27x correspond to the "Low Power IO Controller"?
>>>>On Mon, Jan 26, 2015 at 6:33 PM, Darren Hart <dvhart at linux.intel.com>
>>>>> On 1/26/15, 5:52 PM, "John Hawley" <john.hawley at intel.com> wrote:
>>>>>>On 01/26/2015 05:47 PM, Kevin Shelton wrote:
>>>>>>> On Fri, Jan 23, 2015 at 2:41 PM, John Hawley <john.hawley at intel.com
>>>>>>> <mailto:john.hawley at intel.com>> wrote:
>>>>>>>     > I saw the thread 'Adding an SPI device to the Minnowboard'
>>>>>>>     > 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
>>>>>>>     > the _DSD mechanisms introduced by the ACPI 5.1 specification
>>>>>>>     >
>>>>>>>     > 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
>>>>>>>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
>>>>>>>     on that.  Older kernels without that, likely spidev or a more
>>>>>>>     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
>>>>>>>     > Additional q:
>>>>>>>     > How do you tell the SPI controller that you have an
>>>>>>>     > of the usual active-low device?  Is it correct to do a
>>>>>>>     > 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
>>>>>>> Any debugging ideas?
>>>>>>> What is the best way to learn more about the SPI master?  It's
>>>>>>> into the CPU, correct?
>>>>>>> This smells in the ballpark of
>>>>>>> relatedness:
>>>>>>> I don't grok that patch, but I confirmed my version of pxa2xx.c in
>>>>>>> 3.17 tree appears to contain that change.
>>>>>>The SPI interface is indeed built into the CPU.  It's the pxa2xx
>>>>>>which it looks like you've found.  I'd have to punt to someone else,
>>>>>>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
>>>>> answer to off the top of my head. To find out, I would:
>>>>> 1) Search for other drivers in tree and externally that use
>>>>> 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
>>>>> the same question there
>>>>> --
>>>>> Darren Hart
>>>>> Intel Open Source Technology Center
>>>>> _______________________________________________
>>>>> elinux-MinnowBoard mailing list
>>>>> elinux-MinnowBoard at lists.elinux.org
>>>>> http://lists.elinux.org/mailman/listinfo/elinux-minnowboard
>>> --
>>> Darren Hart
>>> Intel Open Source Technology Center

Darren Hart
Intel Open Source Technology Center

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