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The bam_dma driver needs to know the number of channels and execution environments (EEs) at probe time. If we are in full control of the BAM controller this information can be obtained from the BAM identification registers (BAM_REVISION/BAM_NUM_PIPES). When the BAM is "controlled remotely" it is more complicated. The BAM might not be on at probe time, so reading the registers could fail. This is why the information must be added to the device tree in this case, using "num-channels" and "qcom,num-ees". However, there are also some BAM instances that are initialized by something else but we still have a clock that allows to turn it on when needed. This can be set up in the DT with "qcom,controlled-remotely" and "clocks" and is already supported by the bam_dma driver. Examples for this are the typical BLSP BAM instances on older SoCs, QPIC BAM (for NAND) and the crypto BAM on some SoCs. In this case, there is no need to read "num-channels" and "qcom,num-ees" from the DT. The BAN can be turned on using the clock so we can just read it from the BAM registers like in the normal case. Check for the BAM clock earlier and skip reading "num-channels" and "qcom,num-ees" if it is present to allow simplifying the DT description a bit. Signed-off-by: Stephan Gerhold <stephan@gerhold.net> Reviewed-by: Bhupesh Sharma <bhupesh.sharma@linaro.org> Link: https://lore.kernel.org/r/20230518-bamclk-dt-v2-1-a1a857b966ca@gerhold.net Signed-off-by: Vinod Koul <vkoul@kernel.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.