Hi,

On 28/01/2019 19:10, Mark Brown wrote:
On Sat, Jan 26, 2019 at 05:32:19PM +0100, Jonas Bonn wrote:
@@ -164,6 +166,7 @@ struct spi_device {
        char                    modalias[SPI_NAME_SIZE];
        const char              *driver_override;
        int                     cs_gpio;        /* chip select gpio */
+       uint16_t                word_delay;     /* inter-word delay (us) */
This needs some code in the core joining it up with the per-transfer
word delay similar to what we have for speed_hz and bits_per_word in
__spi_validate().  Then the controller drivers can just look at the
per-transfer value and support both without having to duplicate logic.

So spi_transfer already has a field word_delay and it's defined as 
_clock cycles_ to delay between words.  I defined word_delay in 
spi_device as _microseconds_ to delay along the lines of delay_usecs.
Given that the inter-word delay is a function of the slave device speed 
and not of the SPI bus speed, I'm inclined to say that a time-based 
delay is what we want (to be independent of bus speed).  As such, I want 
to know if I should add word_delay_usecs to _both_ spi_transfer and 
spi_device?
There's only one user of word_delay from spi_transfer.  Just looking at 
it quickly, it looks like it wants the word_delay in 
SPI-controller-clock cycles and not SCK cycles which seems pretty broken 
to me.  Adding Baolin and Lanqing to CC: for comment.  Could we rework 
that to be microseconds and do the calculation in the driver?
Thanks,
Jonas

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