On Wed, Jun 29, 2016 at 08:54:26PM -0700, apronin@chromium.org wrote:

> Some devices may need CS to be deasserted for some time
> between transactions. Added a new capability to guarantee
> a delay between SPI transactions for the device.

This seems like even more of a per device thing - it's a very rare
requirement (I'm guessing for some SPI controller coprocessor) and
there's such a wide range of potential patterns that might be needed
by different devices.  

> +       if (msg->spi->xfer_delay)
> +               mdelay(msg->spi->xfer_delay);
> +
>         spi_set_cs(msg->spi, true);

This isn't a delay between messages, it's a delay before asserting
chip select which will happen every single time we do anything
regardless of if there was any activity immediately before or not.