linux-kernel - Re: [PATCH v2 14/20] mfd: intel_soc_pmic_chtwc: Add intel_cht_wc_get

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Date:   Tue, 16 Nov 2021 12:43:47 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Mark Gross <markgross@...nel.org>,
        Andy Shevchenko <andy@...radead.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Sebastian Reichel <sre@...nel.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Ard Biesheuvel <ardb@...nel.org>, Len Brown <lenb@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Yauhen Kharuzhy <jekhor@...il.com>,
        Tsuchiya Yuto <kitakar@...il.com>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH v2 14/20] mfd: intel_soc_pmic_chtwc: Add
 intel_cht_wc_get_model() helper function

Hi,

On 11/16/21 12:18, Andy Shevchenko wrote:
> On Sun, Nov 14, 2021 at 7:04 PM Hans de Goede <hdegoede@...hat.com> wrote:
>>
>> Tablet / laptop designs using an Intel Cherry Trail x86 main SoC with
>> an Intel Whiskey Cove PMIC do not use a single standard setup for
> 
> does not
> 
>> the charger, fuel-gauge and other chips surrounding the PMIC /
>> charging+data USB port.
>>
>> Unlike what is normal on X86 this diversity in designs is not handled
>> by the ACPI tables. On 2 of the 3 known designs there are no standard
>> (PNP0C0A) ACPI battery devices and on the 3th design the ACPI battery
>> device does not work under Linux due to it requiring non-standard
>> and undocumented ACPI behavior.
>>
>> So to make things work under Linux we use native charger and fuel-gauge
>> drivers on these devices, re-using the native drivers used on ARM boards
>> with the same charger / fuel-gauge ICs.
>>
>> This requires various MFD-cell drivers for the CHT-WC PMIC cells to
>> know which model they are exactly running on so that they can e.g.
>> instantiate an I2C-client for the right model charger-IC (the charger
>> is connected to an I2C-controller which is part of the PMIC).
>>
>> Rather then duplicating DMI-id matching to check which model we are
>> running on in each MFD-cell driver add a helper function for this
>> and make this id all 3 known models:
>>
>> 1. The GPD Win and GPD Pocket mini-laptops, these are really 2 models
>> but the Pocket re-uses the GPD Win's design in a different housing:
>>
>> The WC PMIC is connected to a TI BQ24292i charger, paired with
>> a Maxim MAX17047 fuelgauge + a FUSB302 USB Type-C Controller +
>> a PI3USB30532 USB switch, for a fully functional Type-C port.
>>
>> 2. The Xiaomi Mi Pad 2:
>>
>> The WC PMIC is connected to a TI BQ25890 charger, paired with
>> a TI BQ27520 fuelgauge, using the TI BQ25890 for BC1.2 charger type
>> detection, for a USB-2 only Type-C port without PD.
>>
>> 3. The Lenovo Yoga Book YB1-X90 / Lenovo Yoga Book YB1-X91 series:
>>
>> The WC PMIC is connected to a TI BQ25892 charger, paired with
>> a TI BQ27542 fuelgauge, using the WC PMIC for BC1.2 charger type
>> detection and using the BQ25892's Mediatek Pump Express+ (1.0)
>> support to enable charging with up to 12V through a micro-USB port.
> 
> ...
> 
>> +               /*
>> +                * Note this may not seem like a very unique match, but in the
>> +                * 24000+ DMI decode dumps from linux-hardware.org only 42 have
> 
> Can you add https:// (or is it gopher? :)

linux-hardware.org is intended here as an identifier of the projects, not an
URL. The DMI decode database lives here:

https://github.com/linuxhw/DMI.git

But I don't believe that adding the exact URL in the comment is important,
esp. since that may change over time.

> 
>> +                * a board_vendor value of "AMI Corporation" and of those 42
>> +                * only 1 (the GPD win/pocket entry) has a board_name of
>> +                * "Default string". Also very few devices have both board_ and
>> +                * product_name not set.
>> +                */
> 
> ...
> 
>> +enum intel_cht_wc_models intel_cht_wc_get_model(void)
>> +{
>> +       const struct dmi_system_id *id;
>> +
>> +       id = dmi_first_match(cht_wc_model_dmi_ids);
>> +       if (!id)
>> +               return INTEL_CHT_WC_UNKNOWN;
>> +
>> +       return (long)id->driver_data;
> 
> Why not proper casting, i.e. (enum intel_...)?

Because sizeof(enum) != sizeof(void *) so then the compiler will
complain. Where as sizeof(long) == sizeof(void *)

> 
>> +}
>> +EXPORT_SYMBOL_GPL(intel_cht_wc_get_model);
> 
> Are you planning to use EXPORT_SYMBOL_GPL_NS()? If not, please consider it.

No I was not planning on this and it seems overkill for just a single
exported symbol.

Regards,

Hans