On 2017-04-25 15:47, Jan Kiszka wrote:
> On 2017-04-25 14:30, Mika Westerberg wrote:
>> On Tue, Apr 25, 2017 at 02:17:23PM +0200, Jan Kiszka wrote:
>>> I'm not ACPI guru: How do we come from a SSDT to information that is
>>> carried in the DSDT so far? How can we overload wrong information in the
>>> built in DSDT this way? I'm all ears if we could fix our (and also the
>>> Galileo) quirks like that!
>>
>> SSDT stands for Secondary System Description table which basically adds
>> stuff to DSDT (the main table). Main use for SSDTs is to add devices but
>> you can also amend an existing device in DSDT by adding methods and so
>> forth.
>>
>> In case of Galileo the SPI1 host controller happens to miss _CRS method
>> so we can use SSDT like below to add that method there:
>>
>> Scope (\_SB.PCI0.SPI1)
>> {
>> Name (_CRS, ResourceTemplate () {
>> GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
>> "\\_SB.PCI0.GIP0.GPO", 0) {2} // MUX6_IO
>> })
>>
>> Name (_DSD, Package () {
>> ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>> Package () {
>> Package () {
>> "cs-gpios", Package () {^SPI1, 0, 0, 0},
>> },
>> }
>> })
>> }
>>
>> This effectively means that once the table is parsed we find the SPI1
>> device with two new methods, _CRS and _DSD and the kernel is happy to
>> handle the rest.
>>
>> Important thing here is the
>>
>> Scope (\_SB.PCI0.SPI1)
>>
>> which allows us to reference an object in DSDT.
>>
>
> Ah, now I recall: I think we discussed this before, but for a case were
> we would need to patch an existing element that contains one wrong value
> - that won't work. This case should, though. I'll give that a try.
>
Works fine via an SSDT overlay - perfect!
Now, do you also a suggestion where to put that 5 V reference voltage
value that is hard-coded (via wiring) on the target boards for the ADC?
That is now device-specific, not a controller parameter. Is there an
ACPI-way to express such a parameter?
How would that be done for DTs?
Plan B would be hard-coding in the code for now, waiting for a second,
non-ACPI user to address it.
Jan
--
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Corporate Competence Center Embedded Linux
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