linux-kernel - Re: [PATCH RFC v4 02/15] spi: add basic support for SPI offloading

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Message-ID: <7782352b-b8b3-4f2c-8a6a-b92dab8cb1b6@baylibre.com>
Date: Thu, 24 Oct 2024 09:49:46 -0500
From: David Lechner <dlechner@...libre.com>
To: Nuno Sá <noname.nuno@...il.com>,
 Mark Brown <broonie@...nel.org>, Jonathan Cameron <jic23@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Uwe Kleine-König <ukleinek@...nel.org>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>,
 Lars-Peter Clausen <lars@...afoo.de>, David Jander <david@...tonic.nl>,
 Martin Sperl <kernel@...tin.sperl.org>, linux-spi@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH RFC v4 02/15] spi: add basic support for SPI offloading

On 10/24/24 8:27 AM, Nuno Sá wrote:
> On Wed, 2024-10-23 at 15:59 -0500, David Lechner wrote:
>> Add the basic infrastructure to support SPI offload providers and
>> consumers.
>>

...

>> +struct spi_offload *devm_spi_offload_get(struct device *dev,
>> +					 struct spi_device *spi,
>> +					 const struct spi_offload_config *config)
>> +{
>> +	struct spi_offload *offload;
>> +	int ret;
>> +
>> +	if (!spi || !config)
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	if (!spi->controller->get_offload)
>> +		return ERR_PTR(-ENODEV);
>> +
>> +	offload = spi->controller->get_offload(spi, config);
>> +	if (IS_ERR(offload))
>> +		return offload;
>> +
>> +	if (offload->spi)
>> +		return ERR_PTR(-EBUSY);
>> +
>> +	offload->spi = spi;
>> +	get_device(offload->provider_dev);
> 
> Isn't this redundant? From what I can tell, we're assuming that the spi controller
> (of the spi device) is the offload provider. Therefore, getting an extra reference
> for it does not really seems necessary. The device cannot go away without under the
> spi_device feet. If that could happen, then we would also need to take care about
> callback access and things like that. Going this way, it would also be arguable to
> have a try_module_get().
> 
> - Nuno Sá
> 
> 

Yes, you are right that we don't really need to take a reference to the device.
This was left over from when I made an implementation that assumed the offload
provider could be anything, not just a SPI controller.