Re: [PATCH 5/6] spi: bcm2835: add polling mode for transfers below 30us

[Martin Sperl <kernel@xxxxxxxxxxxxxxxx>]

> On 31.03.2015, at 05:28, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
>> +	/* check if we shall run in polling mode */
>> +	xfer_time_us = tfr->len * 9 * 1000000 / spi_used_hz;
> 
> Why 9 not 8; presumably thats bits per byte, and IIRC SPI doesn't have
> anything like I2C's ack bit per byte?

Well - the bcm2835 make a 1 cycle wait after each byte transferred.
Hence 9 bit actual length we need to account for.

Actually on top of that there are 3 more cycles when bringing the SPI
hardware active (at least with native CS) - but these are minimal
offsets.

Martin


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