Re: [PATCH v3 2/2] iio: adc: ti-ads1298: Add driver

From: Mike Looijmans
Date: Wed Feb 14 2024 - 01:49:01 EST

On 10-02-2024 17:27, Jonathan Cameron wrote:
On Tue, 6 Feb 2024 18:38:29 +0100
Mike Looijmans <mike.looijmans@xxxxxxxx> wrote:

On 06-02-2024 17:32, Andy Shevchenko wrote:
On Tue, Feb 06, 2024 at 04:44:03PM +0100, Mike Looijmans wrote:
On 06-02-2024 16:09, Andy Shevchenko wrote:
On Tue, Feb 06, 2024 at 03:47:45PM +0100, Mike Looijmans wrote:
But it's up to you what to do with that.
Maybe Jonathan can advice something different.
The spinlock also protects the call to spi_async().
I don't get this. Locks usually protect the data and not the code.
Can you elaborate?
Either the DRDY or SPI completion handler will call spi_async(), the
lock assures that it's only called by one.

Arguably it's protecting the destination buffer of the spi_async()
call. We don't really care if we issue two reads (it's a waste
of time and we would store two sets of readings but meh), but we do
care about being sure that don't issue a second read into a buffer
that we are potentially simultaneously getting data back from.

Indeed, that.

There are comments where the release is to describe when it can
be safely unlocked.

I'm not super keen on this whole structure but I don't really have a better
idea. Who builds a device where you have no latched way of seeing
if there is new data? (some) Hardware folk love to assume they have a RTOS only
talking to their device and that no pulse signals will ever be missed.

We get to educate them when ever the opportunity arises :)

Even on RTOS this chip was a pain - to get it to work reliably I had to set up a DMA controller to run the SPI transactions, which took some smart daisy-chaining (I recall having the DMA controller write to its own control registers to avoid involving the CPU).

It's probably possible to trick audio hardware (I2S controller) into grabbing the data (my chip doesn't have that) without involving the CPU.

As the code is now, I can grab data and display it with the IIO oscilloscope over network at 4kHz without losing samples on an A9 at 600Mhz.

Mike Looijmans
System Expert

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