Re: [PATCH 0/1] [x86] BIOS SAR Driver for M.2 Intel Modems

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Shravan S <s.shravan@intel.com>
Cc: Hans de Goede <hdegoede@redhat.com>,
	Mark Gross <mgross@linux.intel.com>,
	Platform Driver <platform-driver-x86@vger.kernel.org>,
	sudhakar.an@intel.com
Subject: Re: [PATCH 0/1] [x86] BIOS SAR Driver for M.2 Intel Modems
Date: Sun, 13 Jun 2021 17:22:22 +0300	[thread overview]
Message-ID: <CAHp75Vfq6B0=q0dsQPTP_A8sdPh9tepBooa7cW=KJYX78ekWtw@mail.gmail.com> (raw)
In-Reply-To: <20210428032224.8299-1-s.shravan@intel.com>

On Fri, Jun 11, 2021 at 12:46 PM Shravan S <s.shravan@intel.com> wrote:
>
> SAR (Specific Absorption Rate) driver is a host driver implemented for Linux
> or chrome platform to limit the exposure of human body to RF frequency by informing
> the Intel M.2 modem to regulate the RF power based on SAR data obtained from the sensors
> captured in the BIOS. ACPI interface exposes this data from the BIOS to SAR driver. The
> front end application in userspace ( eg: Modem Manager) will interact with SAR driver
> to obtain information like the device mode (Example: tablets, laptops, etx), Antenna index,
> baseband index, SAR table index and use available communication like MBIM interface to enable
> data communication to modem for RF power regulation.
>
> The BIOS gets notified about device mode changes through Sensor Driver. This information is
> given to a (newly created) WWAN ACPI function driver when there is a device mode change.
> The driver then uses a _DSM method to retrieve the required information from BIOS.
> This information is then forwarded/multicast to the User-space using the NETLINK interface.
> A lookup table is maintained inside the BIOS which suggests the SAR Table index and Antenna
> Tuner Table Index values for individual device modes.
>
> The SAR parameters to be used on the Modem differs for each Regulatory Mode like FCC, CE and ISED.
> Hence, the SAR parameters are stored separately in the SMBIOS table in the OEM BIOS,
> for each of the Regulatory mode. Regulatory modes will be different based on the region and network
> available in that region.
>
> Hence the entire SAR functionality handling is divided into 2 parts:
>
> •       A ACPI function driver implemented that uses a dedicated ACPI node for WWAN device.
>     sends notifications whenever there is change in Device Mode. (each OEM has different mechanism
>     of updating this DEVICE Mode info). This is notified to User-space applications using
>     the RT-NETLINK interface.
> •       WWAN Device Service listens for RT-NETLINK messages and routes them to Modem using MBIM.

That's a nice feature!
Why is it not a part of some generic subsubsystem under wireless
network subsystem?

-- 
With Best Regards,
Andy Shevchenko