linux-kernel - Re: [PATCH 08/16] i2c: core: Introduce i2c_get_adapter

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Message-ID: <20250408150836.327a337d@bootlin.com>
Date: Tue, 8 Apr 2025 15:08:36 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>, Shawn Guo
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 Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>,
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 Geert Uytterhoeven <geert+renesas@...der.be>, linux-kernel@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-clk@...r.kernel.org, linux-i2c@...r.kernel.org,
 devicetree@...r.kernel.org, linux-pci@...r.kernel.org,
 linux-spi@...r.kernel.org, linux-acpi@...r.kernel.org, Allan Nielsen
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 Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 08/16] i2c: core: Introduce i2c_get_adapter_supplier()

Hi Andy,

On Mon, 7 Apr 2025 18:27:07 +0300
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> On Mon, Apr 07, 2025 at 04:55:37PM +0200, Herve Codina wrote:
> > The supplier device of an I2C adapter is the device that calls
> > i2c_add_adapter() or variants and i2c_del_adapter().
> > 
> > Most of the time this supplier device is the parent of the adapter dev.
> > 
> > Exceptions exist with i2c muxes. Indeed, in case of i2c muxes, the
> > parent of the adapter dev points to the adapter dev the mux is connected  
> 
> dev --> device (in both cases)

Will be updated in the newt iteration.

> 
> > to instead of the supplier of this adapter.
> > 
> > Introduce i2c_get_adapter_supplier() and a new supplier field in the
> > adapter structure in order to ease the adapter supplier retrieval.  
> 
> ...
> 
> > +/**
> > + * i2c_get_adapter_supplier() - Get the supplier of an adapter
> > + * @adapter: the adapter to get the supplier from
> > + *
> > + * return:  
> 
> Return:

Will be updated.

> 
> > + * Look up and return the &struct device corresponding to the device supplying
> > + * this adapter.  
> 
> @adapter

Will be updated.

> 
> > + * The user must call put_device() once done with the supplier returned.
> > + */
> > +struct device *i2c_get_adapter_supplier(struct i2c_adapter *adapter)
> > +{
> > +	return get_device(adapter->supplier ?: adapter->dev.parent);  
> 
> What will be the meaning when both are set? Why dev.parent is not the same
> as supplier in this case?  Looking at the commit message example, it seems
> like you want to provide a physdev or sysdev (as term supplier seems more
> devlink:ish), like it's done elsewhere. And in the same way _always_ initialise
> it. In such a case, the ambiguity will be gone.

When both are set (this is case for i2c muxes), the adapter->supplier the
device that register the I2C adapter using i2c_add_adapter() or variant.
In other word, the device that creates the I2C adapter.

The adapter->dev.parent is most of the time the device that register the
I2C adapter except for i2c muxes. For I2C muxes, this adapter->dev.parent
is the adapter the i2c mux is connected to.

Between physdev and sysdev, I really prefer physdev and, if renaming from
supplier to physdev is still needed (and wanted), I will rename it. Let me
know.

For initialization, I don't want to modify all the I2C controller drivers.
What I can do is to initialize adapter->supplier using adapter->dev.parent
during the i2c_register_adapter() call if it was not already initialize by
the caller (i.e. the I2C controller driver).

Does it make sense ?

Best regards,
Hervé