On 11/24/24 11:38 AM, Jonathan Cameron wrote: > On Fri, 15 Nov 2024 14:18:55 -0600 > David Lechner <dlechner@xxxxxxxxxxxx> wrote: > >> Document SPI offload support for the ad4695 driver. >> >> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx> >> --- >> >> v5 changes: new patch in v5 >> --- >> Documentation/iio/ad4695.rst | 68 ++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 68 insertions(+) >> >> diff --git a/Documentation/iio/ad4695.rst b/Documentation/iio/ad4695.rst >> index 9ec8bf466c15..8009a0c272bc 100644 >> --- a/Documentation/iio/ad4695.rst >> +++ b/Documentation/iio/ad4695.rst >> @@ -47,6 +47,36 @@ In this mode, CNV and CS are tied together and there is a single SDO line. >> To use this mode, in the device tree, omit the ``cnv-gpios`` and >> ``spi-rx-bus-width`` properties. >> >> +SPI offload wiring >> +^^^^^^^^^^^^^^^^^^ >> + >> +When used with a SPI offload, the supported wiring configuration is: >> + >> +.. code-block:: >> + >> + +-------------+ +-------------+ >> + | GP0/BUSY |-------->| TRIGGER | >> + | CS |<--------| CS | >> + | | | | >> + | ADC | | SPI | >> + | | | | >> + | SDI |<--------| SDO | >> + | SDO |-------->| SDI | >> + | SCLK |<--------| SCLK | >> + | | | | >> + | | +-------------+ >> + | CNV |<-----+--| PWM | >> + | | +--| GPIO | >> + +-------------+ +-------------+ >> + >> +In this case, both the ``cnv-gpios`` and ``pwms`` properties are required. >> +The ``#trigger-source-cells = <2>`` property is also required to connect back >> +to the SPI offload. The SPI offload will have ``trigger-sources`` property >> +with cells to indicate the busy signal and which GPx pin is used, e.g >> +``<&ad4695 AD4695_TRIGGER_EVENT_BUSY AD4695_TRIGGER_PIN_GP0>``. >> + >> +.. seealso:: `SPI offload support`_ >> + >> Channel configuration >> --------------------- >> >> @@ -158,6 +188,27 @@ Unimplemented features >> - GPIO support >> - CRC support >> >> +SPI offload support >> +=================== >> + >> +To be able to achieve the maximum sample rate, the driver can be used with the >> +`AXI SPI Engine`_ to provide SPI offload support. >> + >> +.. _AXI SPI Engine: http://analogdevicesinc.github.io/hdl/projects/ad469x_fmc/index.html >> + >> +.. seealso:: `SPI offload wiring`_ >> + >> +When SPI offload is being used, some attributes will be different. >> + >> +* ``trigger`` directory is removed. >> +* ``in_voltage0_sampling_frequency`` attributes are added for setting the sample >> + rate. >> +* ``in_voltage0_sampling_frequency_available`` attributes are added for querying >> + the max sample rate. >> +* ``timestamp`` channel is removed. >> +* Buffer data format may be different compared to when offload is not used, >> + e.g. the ``in_voltage0_type`` attribute. >> + >> Device buffers >> ============== >> >> @@ -165,3 +216,20 @@ This driver supports hardware triggered buffers. This uses the "advanced >> sequencer" feature of the chip to trigger a burst of conversions. >> >> Also see :doc:`iio_devbuf` for more general information. >> + >> +Effective sample rate for buffered reads >> +---------------------------------------- >> + >> +When SPI offload is not used, the sample rate is determined by the trigger that >> +is manually configured in userspace. All enabled channels will be read in a >> +burst when the trigger is received. >> + >> +When SPI offload is used, the sample rate is configured per channel. All >> +all channels will have the same rate, so only one ``sampling_frequency`` > Double all. >> +attribute needs to be set. Since this rate determines the delay between each >> +individual conversion, the effective sample rate for each sample is actually >> +the sum of the periods of each enabled channel in a buffered read. In other >> +words, it is the value of the ``sampling_frequency`` attribute divided by the >> +number of enabled channels. So if 4 channels are enabled, with the >> +``sampling_frequency`` attributes set to 1 MHz, the effective sample rate is >> +250 kHz. > If you are exposing that as a single sampling_frequency I think we should be > adjusting the frequency so it represents the same thing in both modes. There are separate sampling frequency attributes per channel. I wrote "attributes" to try to indicate this. But I was lazy and abbreviated the attribute names. So I can fix that. > > So divide by the number of channels (conversely run faster if more channels > enabled). > > Jonathan >> >
