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Message-ID: <aBK6Zlx71Aeihue/@JSANTO12-L01.ad.analog.com>
Date: Wed, 30 Apr 2025 21:03:50 -0300
From: Jonathan Santos <jonath4nns@...il.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-gpio@...r.kernel.org, andy@...nel.org, nuno.sa@...log.com,
Michael.Hennerich@...log.com, marcelo.schmitt@...log.com,
jic23@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
conor+dt@...nel.org, marcelo.schmitt1@...il.com,
linus.walleij@...aro.org, brgl@...ev.pl, lgirdwood@...il.com,
broonie@...nel.org, dlechner@...libre.com
Subject: Re: [PATCH v6 08/11] iio: adc: ad7768-1: add support for
Synchronization over SPI
On 04/28, Andy Shevchenko wrote:
> On Mon, Apr 28, 2025 at 3:14 AM Jonathan Santos
> <Jonathan.Santos@...log.com> wrote:
> >
> > The synchronization method using GPIO requires the generated pulse to be
> > truly synchronous with the base MCLK signal. When it is not possible to
> > do that in hardware, the datasheet recommends using synchronization over
> > SPI, where the generated pulse is already synchronous with MCLK. This
> > requires the SYNC_OUT pin to be connected to SYNC_IN pin.
>
> to the SYNC_IN
>
> > Use trigger-sources property to enable device synchronization over SPI
> > and multi-device synchronization, as an alternative to adi,sync-in-gpios
> > property.
>
> ...
>
> > +static int ad7768_send_sync_pulse(struct ad7768_state *st)
> > +{
> > + if (st->en_spi_sync)
> > + return regmap_write(st->regmap, AD7768_REG_SYNC_RESET, 0x00);
>
> > + if (st->gpio_sync_in) {
>
> Dup check, the following have already it.
>
> > + gpiod_set_value_cansleep(st->gpio_sync_in, 1);
>
> Yes, I see the original code, but still the Q is why no delay. Perhaps
> a comment explaining that the GPIO op is slow enough (?) to add.
>
Datasheet specifies a minimum of 1.5*Tmclk pulse width. For the
recommended mclk of 16.384 MHz, it usually takes 4 times the minimum
pulse width. If it can be less than that for other plataforms I can add
this delay.
> > + gpiod_set_value_cansleep(st->gpio_sync_in, 0);
> > + }
> > +
> > + return 0;
> > +}
>
> ...
>
> > +static struct gpio_desc *ad7768_trigger_source_get_gpio(struct device *dev,
> > + struct fwnode_handle *fwnode)
> > +{
> > + const char *value;
> > + int ret;
> > +
> > + ret = fwnode_property_read_string(fwnode, "compatible", &value);
> > + if (ret)
> > + return ERR_PTR(ret);
> > +
> > + if (strcmp("gpio-trigger", value))
> > + return ERR_PTR(-EINVAL);
>
> Reinvention of fwnode_device_is_compatible().
>
Thanks!
> > + return devm_fwnode_gpiod_get_index(dev, fwnode, NULL, 0,
> > + GPIOD_OUT_LOW, "sync-in");
> > +}
>
> ...
>
> > +static int ad7768_trigger_sources_get_sync(struct device *dev,
> > + struct ad7768_state *st)
> > +{
> > + struct fwnode_reference_args args;
> > + struct fwnode_handle *fwnode = NULL;
>
> Redundant assignment AFAICS.
>
> > + int ret;
> > +
> > + /*
> > + * The AD7768-1 allows two primary methods for driving the SYNC_IN pin
> > + * to synchronize one or more devices:
> > + * 1. Using an external GPIO.
> > + * 2. Using a SPI command, where the SYNC_OUT pin generates a
> > + * synchronization pulse that drives the SYNC_IN pin.
> > + */
> > + if (!device_property_present(dev, "trigger-sources")) {
> > + /*
> > + * In the absence of trigger-sources property, enable self
> > + * synchronization over SPI (SYNC_OUT).
> > + */
> > + st->en_spi_sync = true;
> > + return 0;
> > + }
> > +
> > + ret = fwnode_property_get_reference_args(dev_fwnode(dev),
>
> In this case the above is better to be also fwnode_property_present().
> You save a double call to dev_fwnode().
>
> > + "trigger-sources",
> > + "#trigger-source-cells",
> > + 0,
> > + AD7768_TRIGGER_SOURCE_SYNC_IDX,
> > + &args);
> > + if (ret)
> > + return ret;
> > +
> > + fwnode = args.fwnode;
> > + /*
> > + * First, try getting the GPIO trigger source and fallback to
> > + * synchronization over SPI in case of failure.
> > + */
> > + st->gpio_sync_in = ad7768_trigger_source_get_gpio(dev, fwnode);
> > + if (IS_ERR(st->gpio_sync_in)) {
> > + /*
> > + * For this case, it requires one argument, which indicates the
> > + * output pin referenced.
> > + */
> > + if (args.nargs < 1)
> > + goto err_not_supp;
> > +
> > + if (args.args[0] != AD7768_TRIGGER_SOURCE_SYNC_OUT)
> > + goto err_not_supp;
> > +
> > + /*
> > + * Only self trigger is supported for now, i.e.,
> > + * external SYNC_OUT is not allowed.
> > + */
> > + if (fwnode->dev == dev) {
>
> ?!?! What is this?!
>
> For the reference:
> https://elixir.bootlin.com/linux/v6.15-rc3/source/include/linux/fwnode.h#L51
>
I see, my bad. I will follow David's suggestion, so we will avoid this.
> > + st->en_spi_sync = true;
> > + goto out_put_node;
> > + }
> > +
> > + goto err_not_supp;
> > + }
> > +
> > + goto out_put_node;
> > +
> > +err_not_supp:
> > + ret = dev_err_probe(dev, -EOPNOTSUPP,
> > + "Invalid synchronization trigger source");
>
> Missing \n, and can be one line anyway (we don't complain about long
> strings ending with string literals for ages, way before the 100
> character limit).
>
> > +out_put_node:
> > + fwnode_handle_put(args.fwnode);
> > + return ret;
> > +}
>
> --
> With Best Regards,
> Andy Shevchenko
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