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    SubjectRe: [PATCH 5/9] mfd: Add UART support for the ST-Ericsson CG2900.
    From
    Par,

    > Well, from what I can see LL is an extension of the H4, basically it
    > adds sleep mode handling in a vendor specific way to the normal H4
    > protocol. So it is also based on the hci_h4 just as our file is. But
    > our file has basically nothing in common with what has been for the LL
    > file. We don't support any of the LL sleep commands for example.
    > So if I would make a driver for a combo chip supporting LL, I would
    > either modify the existing hci_ll.c or I would make a new file based
    > on hci_ll.c. There is not much you could really reuse from our new
    > file. Basically it would be the handling of any common channels, so if
    > you would for example have the same specification of FM and GPS you
    > could maybe save around 20 lines of common code, but you would
    > probably have to add a lot of more code just to keep the solution
    > generic.

    Right, but this gives me the hard time seeing how your implementation
    is applicable to other multi-functional chips with similar
    functionality.

    > One major difference is also that hci_ll never changes baud rate or
    > other settings. I assume that is done from hciattach during startup
    > instead. But we cannot run with that since we have to shut down the
    > chip when no user is connected in order to save power. This means that
    > we have to add vendor specific commands in order to for example set
    > baud rate. And then you run into these vendor specific problems. If
    > there would be a standardized specification on how to set baud rate
    > and how to put chip in sleep I assume things could be solved
    > differently, but that is not the case.

    Again, there are at least TI and Broadcom chips that support HCI_LL
    and if they were to use your implementation of the core, they would
    have had to add 2 more implementations of the corresponding line
    discipline driver.

    > As a quick answer to your question: that would depend on the
    > difference between the different controllers, I guess. But CG2900
    > doesn't support the LL protocol so it is not an issue for that.

    Right, but if you are only aiming cg2000, why would you create a
    framework for that? I initially thought your solution was generic
    enough to handle other "many-in-one" Bluetooth chips but I'm
    completely unsure about that now.

    Thanks,
    Vitaly


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