Re: [PATCH RFC] spi: add flow controll support

[Martin Sperl <martin@xxxxxxxxx>]

> 
> On 29.02.2016, at 13:04, Oleksij Rempel <linux@xxxxxxxxxxxxxxxx> wrote:
> 
> Different HW implement different variants of SPI based flow control (FC).
> To flexible FC implementation a spited it to fallowing common parts:
> Flow control: Request Sequence
> Master CS   |-------2\_____________________|
> Slave  FC   |-----1\_______________________|
> DATA        |-----------3\_________________|
> 
> Flow control: Ready Sequence
> Master CS   |-----1\_______________________|
> Slave  FC   |--------2\____________________|
> DATA        |-----------3\_________________|
> 
> Flow control: ACK End of Data
> Master CS   |______________________/2------|
> Slave  FC   |________________________/3----|
> DATA        |__________________/1----------|
> 
> Flow control: Pause
> Master CS   |_______________________/------|
> Slave  FC   |_______1/-----\3______/-------|
> DATA        |________2/------\4___/--------|

The MAX187/189 SPI-ADC implements a different kind of
flow control that is signaling inline on DATA/MISO:

Master CS   |-----1\_______________________|
MISO/DATA   |------2\____3/----------------|
CONV START  |       ^                      |
DATA READY  |             ^                |

So when CS get asserted (1) 
MISO/DATA becomes dominant low (2) and the ADC conversion starts
  (within 100ns of (1))
When MISO/DATA goes dominant high (3) then the conversion has finished
and the transfer may start.

A flow-control interface should also cover similar cases - or
at least get designed so that such a case can also get handled
by the framework in the future as well.

> +
> +/* spi_fc_probe should be called by spi_device driver. */
> +int spi_fc_probe(struct spi_device *spi)
> ...
> +}
> +EXPORT_SYMBOL_GPL(spi_fc_probe);

Please add kernel doc to the exported methods

Please put per driver changes into a separate patch.

Also missing from the patch(set) is the dt-bindings documentation - 
see Documentation/devicetree/bindings/spi/spi-bus.txt.

Martin
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