linux-kernel - Re: [PATCH v6 8/8] iio: dac: adi-axi-dac: add registering of child fdt node

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Message-ID: <df1cdac2c954d9a95b9026a400e68697e177787f.camel@gmail.com>
Date: Tue, 15 Oct 2024 08:11:46 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: David Lechner <dlechner@...libre.com>, Angelo Dureghello
 <adureghello@...libre.com>, Nuno Sá
 <nuno.sa@...log.com>,  Lars-Peter Clausen <lars@...afoo.de>, Michael
 Hennerich <Michael.Hennerich@...log.com>,  Jonathan Cameron
 <jic23@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Olivier Moysan
 <olivier.moysan@...s.st.com>
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v6 8/8] iio: dac: adi-axi-dac: add registering of child
 fdt node

On Mon, 2024-10-14 at 16:16 -0500, David Lechner wrote:
> On 10/14/24 5:08 AM, Angelo Dureghello wrote:
> > From: Angelo Dureghello <adureghello@...libre.com>
> > 
> > Change to obtain the fdt use case as reported in the
> > adi,ad3552r.yaml file in this patchset.
> > 
> > The DAC device is defined as a child node of the backend.
> > Registering the child fdt node as a platform devices.
> > 
> > Signed-off-by: Angelo Dureghello <adureghello@...libre.com>
> > ---
> >  drivers/iio/dac/adi-axi-dac.c | 53 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 53 insertions(+)
> > 
> > diff --git a/drivers/iio/dac/adi-axi-dac.c b/drivers/iio/dac/adi-axi-dac.c
> > index b887c6343f96..f85e3138d428 100644
> > --- a/drivers/iio/dac/adi-axi-dac.c
> > +++ b/drivers/iio/dac/adi-axi-dac.c
> > @@ -29,6 +29,8 @@
> >  #include <linux/iio/buffer.h>
> >  #include <linux/iio/iio.h>
> >  
> > +#include "ad3552r-hs.h"
> > +
> >  /*
> >   * Register definitions:
> >   *   https://wiki.analog.com/resources/fpga/docs/axi_dac_ip#register_map
> > @@ -738,6 +740,39 @@ static int axi_dac_bus_reg_read(struct iio_backend *back,
> > u32 reg, u32 *val,
> >  	return regmap_read(st->regmap, AXI_DAC_CUSTOM_RD_REG, val);
> >  }
> >  
> > +static void axi_dac_child_remove(void *data)
> > +{
> > +	struct platform_device *pdev = data;
> > +
> > +	platform_device_unregister(pdev);

Just do platform_device_unregister(data)... Or call the argument pdev for better
readability...

> > +}
> > +
> > +static int axi_dac_create_platform_device(struct axi_dac_state *st,
> > +					  struct fwnode_handle *child)
> > +{
> > +	struct ad3552r_hs_platform_data pdata = {
> > +		.bus_reg_read = axi_dac_bus_reg_read,
> > +		.bus_reg_write = axi_dac_bus_reg_write,
> > +	};
> > +	struct platform_device_info pi = {
> > +		.parent = st->dev,
> > +		.name = fwnode_get_name(child),
> > +		.id = PLATFORM_DEVID_AUTO,
> > +		.fwnode = child,
> > +		.data = &pdata,
> > +		.size_data = sizeof(pdata),
> > +	};
> > +	struct platform_device *pdev;
> > +
> > +	pdev = platform_device_register_full(&pi);
> > +	if (IS_ERR(pdev))
> > +		return PTR_ERR(pdev);
> > +
> > +	device_set_node(&pdev->dev, child);
> 
> Not sure why Nuno suggested adding device_set_node(). It is
> redundant since platform_device_register_full() already does
> the same thing.
> 

Indeed... I realized that yesterday when (actually) looking at
platform_device_register_full(). You just beat me in replying to the email. Sorry for
the noise...

> (And setting it after platform_device_register_full() would
> be too late anyway since drivers may have already probed.)

> > +
> > +	return devm_add_action_or_reset(st->dev, axi_dac_child_remove, pdev);
> > +}
> > +
> >  static const struct iio_backend_ops axi_dac_generic_ops = {
> >  	.enable = axi_dac_enable,
> >  	.disable = axi_dac_disable,
> > @@ -874,6 +909,24 @@ static int axi_dac_probe(struct platform_device *pdev)
> >  		return dev_err_probe(&pdev->dev, ret,
> >  				     "failed to register iio backend\n");
> >  
> > +	device_for_each_child_node_scoped(&pdev->dev, child) {
> > +		int val;
> > +

I'm starting to come around again if some sort of flag (bus_controller or an explicit
has_child) wouldn't make sense (since you may need to re-spin another version). So we
could error out in case someone comes up with child nodes on a device that does not
support them. 

Anyways, I'll leave this up to you and maybe others can also argue about this...

> > +		/* Processing only reg 0 node */
> > +		ret = fwnode_property_read_u32(child, "reg", &val);
> > +		if (ret)
> > +			return dev_err_probe(&pdev->dev, ret,
> > +						"child node missing.");
> 
> Shouldn't the error message say that there is a problem with the reg
> property? We already have a handle to the child node, so the child node
> isn't missing.

Makes sense... like "reg property missing" - something on those lines.

- Nuno Sá