linux-kernel - Re: [PATCH v4 06/13] iio: dac: ds4424: use device match data for chip info

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Message-ID: <aYWe0-2KMLijFVh6@pengutronix.de>
Date: Fri, 6 Feb 2026 08:57:07 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Andy Shevchenko <andriy.shevchenko@...el.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	David Jander <david@...tonic.nl>
Subject: Re: [PATCH v4 06/13] iio: dac: ds4424: use device match data for
 chip info

On Thu, Feb 05, 2026 at 08:43:25PM +0000, Jonathan Cameron wrote:
> On Tue, 3 Feb 2026 16:56:00 +0200
> Andy Shevchenko <andriy.shevchenko@...el.com> wrote:
> 
> > On Tue, Feb 03, 2026 at 01:00:02PM +0100, Oleksij Rempel wrote:
> > > On Tue, Feb 03, 2026 at 01:51:23PM +0200, Andy Shevchenko wrote:  
> > > > On Tue, Feb 03, 2026 at 11:17:42AM +0100, Oleksij Rempel wrote:  
> > > > > On Tue, Feb 03, 2026 at 12:03:23PM +0200, Andy Shevchenko wrote:  
> > > > > > On Tue, Feb 03, 2026 at 10:34:26AM +0100, Oleksij Rempel wrote:  
> > 
> > ...
> > 
> > > > > > > -	indio_dev->name = id->name;  
> > > > > >   
> > > > > > > +	indio_dev->name = client->name;  
> > > > > > 
> > > > > > Isn't this an ABI breakage?  
> > > > > 
> > > > > I can't confirm it.
> > > > > 
> > > > > before all patches:
> > > > > root@...troKit:~ cat /sys/bus/iio/devices/iio:device3/name 
> > > > > ds4424
> > > > > 
> > > > > after:
> > > > > root@...troKit:~ cat /sys/bus/iio/devices/iio:device3/name 
> > > > > ds4424  
> > > > 
> > > > In ACPI case it might look differently, but I have no means to test this.
> > > > 
> > > > id->name comes strictly from an i2c table, while client->name is constructed
> > > > using specifics of the firmware enumeration. In DT due to some (historical?)
> > > > reasons the client->name has no vendor substring and hence matches 1:1 to
> > > > id->name. In ACPI, IIRC, the client->name is ACPI device instance name,
> > > > something like ABCD0123:00.  
> > > 
> > > Ok, I see. Should I revert this line?  
> > 
> > Just do not introduce that change (change of the ->name field) in the original
> > patch, in that case no revert churn would be needed.
> > 
> I think this got dealt with in discussion of next version but
> safest route is just have an extra copy of the name in the
> chip_info structure.  Then we know it's stable against different
> firmware types etc.

Something like this?

diff --git a/drivers/iio/dac/ds4424.c b/drivers/iio/dac/ds4424.c
index ccf36d3e0443..ffa65b22a1fd 100644
--- a/drivers/iio/dac/ds4424.c
+++ b/drivers/iio/dac/ds4424.c
@@ -50,6 +50,7 @@
 }
 
 struct ds4424_chip_info {
+	const char *name;
 	int vref_mV;
 	int scale_denom;
 	u8 result_mask;
@@ -57,6 +58,7 @@ struct ds4424_chip_info {
 };
 
 static const struct ds4424_chip_info ds4402_info = {
+	.name = "ds4402",
 	.vref_mV = 1230,
 	.scale_denom = 4,
 	.result_mask = DS4404_DAC_MASK,
@@ -64,6 +66,7 @@ static const struct ds4424_chip_info ds4402_info = {
 };
 
 static const struct ds4424_chip_info ds4404_info = {
+	.name = "ds4404",
 	.vref_mV = 1230,
 	.scale_denom = 4,
 	.result_mask = DS4404_DAC_MASK,
@@ -71,6 +74,7 @@ static const struct ds4424_chip_info ds4404_info = {
 };
 
 static const struct ds4424_chip_info ds4422_info = {
+	.name = "ds4422",
 	.vref_mV = 976,
 	.scale_denom = 16,
 	.result_mask = DS4424_DAC_MASK,
@@ -78,6 +82,7 @@ static const struct ds4424_chip_info ds4422_info = {
 };
 
 static const struct ds4424_chip_info ds4424_info = {
+	.name = "ds4424",
 	.vref_mV = 976,
 	.scale_denom = 16,
 	.result_mask = DS4424_DAC_MASK,
@@ -335,7 +340,7 @@ static int ds4424_probe(struct i2c_client *client)
 
 	data = iio_priv(indio_dev);
 	i2c_set_clientdata(client, indio_dev);
-	indio_dev->name = id->name;
+	indio_dev->name = chip_info->name;
 	data->chip_info = chip_info;
 
 	data->vcc_reg = devm_regulator_get(&client->dev, "vcc");


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