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@xxxxxxxxxx> 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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