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    SubjectRe: [PATCH] spi: spi-geni-qcom: Add SPI driver support for GENI based QUP
    On Fri, Aug 10, 2018 at 08:40:17AM -0700, Doug Anderson wrote:
    > On Fri, Aug 10, 2018 at 3:52 AM, Mark Brown <broonie@kernel.org> wrote:

    > > This is more about matching the data rate between the two drivers - the
    > > clock framework could (and possibly should) reasonably return an error
    > > here, we're trying to ensure that drivers and controllers work well
    > > together here.

    > The clock framework should be able to accomplish what you want. If
    > you just request the rate it will do its best to make the rate
    > requested. If we want to see what clock would be set before setting

    The request could be massively off the deliverable rate - 50% or more.

    > is "close enough" in this case? I haven't gone and dug, but I've
    > always seen people only specify a max rate for SPI. ...so as long as
    > the clock framework gives us something <= the clock we requested then
    > we should be OK, right? If / when this becomes a problem then we
    > should add a min/max to "struct spi_transfer", no?

    On the other hand if I ask for my audio to be played at 44.1kHz and the
    clock framework says "yes, sure" and gives me 8kHz then the user
    experience will be poor.

    > Note that there are also clk_set_rate_range(), clk_set_min_rate(), and
    > clk_set_max_rate() though I'm told those might be a bit quirky.

    They're certainly not widely used at any rate.

    > ...but maybe we don't need to argue about this anyway since IMHO we
    > should just use the clk framework to figure out our maximum speed.

    It looks like that's true in this case.

    > >> 3. If you really truly need code in the SPI driver then make sure you
    > >> include a compatible string for the SoC and have a table in the driver
    > >> that's found with of_device_get_match_data(). AKA:

    > >> compatible = "qcom,geni-spi-sdm845", "qcom,geni-spi";

    > > A controller driver really shouldn't need to be open coding anything.

    > It wouldn't be open-coding, it would be a different way of specifying
    > things. In my understanding it's always a judgement call about how

    If you're saying we need clock rate selection logic (which is what it
    sounds like) rather than data then that seems like a problem.
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