linux-kernel - Re: [PATCH] iio: adc: Add support for TI ADC1x8s102

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Message-ID: <ca23678c-be8c-1e3f-4688-67b29770c99b@siemens.com>
Date:   Tue, 25 Apr 2017 15:47:17 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sascha Weisenberger <sascha.weisenberger@...mens.com>
Subject: Re: [PATCH] iio: adc: Add support for TI ADC1x8s102

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.

Thanks,
Jan

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