On Fri, Feb 26, 2016 at 10:31:50AM +0800, Huang, Tao wrote:
> You misunderstand me. I talk about spi_setup, as
> Documentation/spi/spi-summary, which would normally be called from
> probe() before the first I/O is done to the device.
> spi_setup will call spi_set_cs(spi, false), which introduced with commit
> 1a7b7ee72c21 ("spi: Ensure that CS line is in non-active state after
> spi_setup()"). And spi_set_cs will call spi->master->set_cs, and set_cs
> callback will access register. Without clk enable, I believe some
> drivers will failed to run.That's definitely very driver specific, a large proportion of devices don't manage their chip selects via the SPI controller at all.
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