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The Samsung Galaxy A3/A5 both have a Samsung S3FWRN5 NFC chip that works quite well with the s3fwrn5 driver in the Linux NFC subsystem. The clock setup for the NFC chip is a bit special (although this seems to be a common approach used for Qualcomm devices with NFC): The NFC chip has an output GPIO that is asserted whenever the clock is needed to function properly. On the A3/A5 this is wired up to PM8916 GPIO2, which is then configured with a special function (NFC_CLK_REQ or BB_CLK2_REQ). Enabling the rpmcc RPM_SMD_BB_CLK2_PIN clock will then instruct PM8916 to automatically enable the clock whenever the NFC chip requests it. The advantage is that the clock is only enabled when needed and we don't need to manage it ourselves from the NFC driver. Note that for some reason Samsung decided to connect the I2C pins to GPIOs where no hardware I2C bus is available, so we need to fall back to software bit-banging with i2c-gpio. Cc: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com> Signed-off-by: Stephan Gerhold <stephan@gerhold.net> Link: https://lore.kernel.org/r/20210604172742.10593-5-stephan@gerhold.net Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.