linux-kernel - Re: [PATCH v8 01/17] spi: add basic support for SPI offloading

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Message-ID: <27d2a88c-b44a-4712-b066-b999e41774f0@baylibre.com>
Date: Mon, 10 Feb 2025 11:11:23 -0600
From: David Lechner <dlechner@...libre.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: 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>, 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, Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v8 01/17] spi: add basic support for SPI offloading

On 2/10/25 10:45 AM, Andy Shevchenko wrote:
> On Fri, Feb 07, 2025 at 02:08:58PM -0600, David Lechner wrote:
>> Add the basic infrastructure to support SPI offload providers and
>> consumers.
>>
>> SPI offloading is a feature that allows the SPI controller to perform
>> transfers without any CPU intervention. This is useful, e.g. for
>> high-speed data acquisition.
>>
>> SPI controllers with offload support need to implement the get_offload
>> and put_offload callbacks and can use the devm_spi_offload_alloc() to
>> allocate offload instances.
>>
>> SPI peripheral drivers will call devm_spi_offload_get() to get a
>> reference to the matching offload instance. This offload instance can
>> then be attached to a SPI message to request offloading that message.
>>
>> It is expected that SPI controllers with offload support will check for
>> the offload instance in the SPI message in the ctlr->optimize_message()
>> callback and handle it accordingly.
>>
>> CONFIG_SPI_OFFLOAD is intended to be a select-only option. Both
>> consumer and provider drivers should `select SPI_OFFLOAD` in their
>> Kconfig to ensure that the SPI core is built with offload support.
> 
> (I know that this is now in SPI tree, but still we have time to address something)
> 
>> +++ b/include/linux/spi/offload/consumer.h
> 
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Copyright (C) 2024 Analog Devices Inc.
>> + * Copyright (C) 2024 BayLibre, SAS
>> + */
>> +
>> +#ifndef __LINUX_SPI_OFFLOAD_CONSUMER_H
>> +#define __LINUX_SPI_OFFLOAD_CONSUMER_H
>> +
>> +#include <linux/module.h>
>> +#include <linux/spi/offload/types.h>
>> +#include <linux/types.h>
> 
>> +MODULE_IMPORT_NS("SPI_OFFLOAD");
> 
> This diminishes the point of the namespaces. Anybody who includes a (dangling)
> header gets namespace imported, which is not good. Same for other globally
> visible headers.
> 
> (This is the main concern of this patch).

In this case, we specifically split up the headers so that the only time you
would ever include this header is if you need to call functions in this
namespace (i.e. struct definitions are in linux/spi/offload/types.h which
doesn't import the namespace). So this doesn't actually seem like a problem
to me.