[MinnowBoard] SPI questions

Thu Jan 29 00:19:03 UTC 2015

through liberal sprinkling of printks I find that when spi_new_device
gets called in my board file, eventually setup_cs gets called in
drivers/spi/spi-pxa2xx.c, but setup_cs returns before it can set
gpio_cs_inverted because chip_info is NULL

Should board files define a pxa2xx_spi_chip struct (I see this done in
arch/arm/mach-pxa/hx4700.c)?

Am I correct in calling hx4700.c a board file?

On Tue, Jan 27, 2015 at 9:21 PM, Darren Hart <dvhart at linux.intel.com> wrote:
> 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.
>
> --
> Darren
>
>
> 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>
>>wrote:
>>> 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>
>>>wrote:
>>>> 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
>>>>>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 <dvhart at linux.intel.com>
>>>>>wrote:
>>>>>> 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'
>>>>>>>>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/2634
>>>>>>>>67.
>>>>>>>>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
>>>>>> 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
>
>
>