linux-kernel - Re: [PATCH v3 -next 1/5] spi: mockup: Add SPI controller testing driver

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Message-ID: <ZUjVBKuviXwM0aiR@finisterre.sirena.org.uk>
Date:   Mon, 6 Nov 2023 11:59:00 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Zhang Xiaoxu <zhangxiaoxu@...weicloud.com>
Cc:     zhangxiaoxu5@...wei.com, weiyongjun1@...wei.com,
        rostedt@...dmis.org, mingo@...hat.com, frowand.list@...il.com,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 -next 1/5] spi: mockup: Add SPI controller testing
 driver

On Sat, Nov 04, 2023 at 02:46:46PM +0800, Zhang Xiaoxu wrote:

> This is accomplished by executing the following command:
> 
> $ echo adcxx1s 0 > /sys/class/spi_master/spi0/new_device

That's not a valid sysfs format, sysfs requires one value per file.
configfs might be a better fit?

> +config SPI_MOCKUP
> +	tristate "SPI controller Testing Driver"
> +	depends on OF

Why would this depend on DT?  Given that any test SPI controller is a
virtual device it should never appear in DT and we probably shouldn't
require providing DT for the created devices even if we implement
support for that, only some devices might care.
`
> +++ b/drivers/spi/spi-mockup.c
> @@ -0,0 +1,211 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * SPI controller Testing Driver
> + *
> + * Copyright(c) 2022 Huawei Technologies Co., Ltd.
> + */

Please keep the entire comment a C++ one so things look more
intentional.

> +#define MOCKUP_CHIPSELECT_MAX		8

Why would we have a hard coded limit here?

> +	blank = strchr(buf, ' ');
> +	if (!blank) {
> +		dev_err(dev, "%s: Extra parameters\n", "new_device");
> +		return -EINVAL;
> +	}

There is no point in using %s to render a constant string.

> +static const struct of_device_id spi_mockup_match[] = {
> +	{ .compatible = "spi-mockup", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, spi_mockup_match);

If we were going to instantiate this via DT we'd need a binding, but as
I indicated above since this is purely virtual and not even something
like virtual hardware provided by a VMM but rather just something kernel
internal we should probably not be using DT at all.  Providing a device
facing DT interface might be useful, but that's a second stage thing.

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