Date:   Sun, 11 Aug 2019 13:09:59 +1000
From:   Andrew Cooks <acooks@...ionali.st>
To:     Jean Delvare <jdelvare@...e.de>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
Cc:     Linux I2C <linux-i2c@...r.kernel.org>,
        Wolfram Sang <wsa@...-dreams.de>, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, platypus-sw@...ngear.com,
        "Tobin C . Harding" <me@...in.cc>,
        Guenter Roeck <linux@...ck-us.net>,
        Will Wagner <willw@...allon.com>
Subject: Re: [PATCH v5 0/3] Enable ACPI-defined peripherals on i2c-piix4 SMBus


On 8/9/19 6:33 PM, Jean Delvare wrote:
> Hi Enrico,
>
> On Thu, 8 Aug 2019 11:17:53 +0200, Enrico Weigelt, metux IT consult wrote:
>> On 02.08.19 14:51, Jean Delvare wrote:
>>> These patches fix a couple of issues with the i2c-piix4 driver on
>>> AMD Family 16h Model 30h SoCs and add ACPI-based enumeration to the
>>> i2c-piix4 driver.  
>> Can you tell a little bit more about what devices are behind the smbus ?
>> I recall the G-412 SoCs (such as on apu2+ boards) have an Hudson inside
>> and fall into this category. (I'll have to check when back in office),
>> so (as the apu2 platform driver maintainer) I'm very interested in this.
> Unfortunately not. I only picked up from where Andrew Cooks left, due
> to me being way too slow to review his patches. I did not want his work
> to be lost. I was able to test the first 2 patches which fix bugs, but
> not the 3rd one which deals with ACPI devices. There does not seem to
> be any such device on the 2 test machines I have remotely access to.

Thanks for taking a look at these patches and thanks for your many years of support and maintenance.

The patches I submitted were developed for an commercial product, but I am not with the company anymore and do not have access to the hardware. This is the device: https://opengear.com/products/om2200-operations-manager/

The specific peripheral that required ACPI support is the NCT7491, and a driver is available at https://github.com/opengear/nct7491-driver

>> Does the probing need some special BIOS support (or do the necessary
>> table entries already come from aegesa) ?
> I assume that ACPI devices are declared in one of the ACPI tables, so
> it comes from the "BIOS", yes, whatever form it takes these days.
Yes, though unfortunately I didn't get a chance to submit this to the coreboot project and no longer have access to the source.
>
>> I have to admit, I'm still confused by the AMD documentation - haven't
>> found a clear documentation on what peripherals exactly are in the
>> G-412 SoC, just puzzled together that the FCH seems to be an Hudson,
>> probably v2. There also seems to be some relation between smbus and
>> gpio, but the gpio's are directly memory-mapped - no idea whether they
>> just share the same base address register or the gpios are really behind
>> smbus and some hw logic directy maps them into mmio space ...
>> Do you happen to have some more information on that ?
> I remember noticing long ago that SMBus ports were using GPIO pins, so
> these pins could be used for SMBus or for any other purpose. I could
> not find any way to figure out from the registers if a given pin pair
> was used for SMBus or not, which is pretty bad because it means we are
> blindly instantiating ALL possible SMBus ports even if some of the pins
> are used for a completely different purpose. It was over 1 year ago
> though, so I don't remember the details, and my findings then may not
> apply to the most recent hardware.
>
>> By the way: I'm considering collecting some hw documentation in the
>> kernel tree (maybe Documentation/hardware/...) - do you folks think
>> that's a good idea ?
> No. Only documentation specifically related to the Linux kernel should
> live in the kernel tree. OS-neutral documentation must go somewhere
> else.
>
Thanks,

Andrew

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