linux-kernel - Re: [RFC PATCH v2] fpga: Introduce new fpga subsystem

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Date:	Wed, 02 Oct 2013 09:06:36 -0700
From:	Joe Perches <joe@...ches.com>
To:	Michal Simek <michal.simek@...inx.com>
Cc:	linux-kernel@...r.kernel.org, monstr@...str.eu,
	Alan Tull <atull@...era.com>, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dinh Nguyen <dinguyen@...era.com>,
	Philip Balister <philip@...ister.org>,
	Alessandro Rubini <rubini@...dd.com>,
	Steffen Trumtrar <s.trumtrar@...gutronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Jason Cooper <jason@...edaemon.net>,
	Yves Vandervennet <rocket.yvanderv@...il.com>,
	Kyle Teske <kyle.teske@...com>,
	Josh Cartwright <joshc@....teric.us>,
	Rob Landley <rob@...dley.net>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cesar Eduardo Barros <cesarb@...arb.net>,
	"David S. Miller" <davem@...emloft.net>,
	David Brown <davidb@...eaurora.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Nicolas Pitre <nico@...aro.org>,
	Mark Langsdorf <mark.langsdorf@...xeda.com>,
	Felipe Balbi <balbi@...com>, linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH v2] fpga: Introduce new fpga subsystem

On Wed, 2013-10-02 at 17:35 +0200, Michal Simek wrote:
> This new fpga subsystem core should unify all fpga drivers/managers which
> do the same things. Load configuration data to fpga or another programmable
> logic through common interface. It doesn't matter if it is MMIO device,
> gpio bitbanging, etc. connection. The point is to have the same
> interface for these drivers.

Does this interface support partial reprogramming/configuration
for FPGAs that can do that?

trivial notes:

There are a _lot_ of dev_dbg statements.

I hope some of these would be removed one day,
especially the function tracing style ones, because
there's already a generic kernel mechanism for that.

Maybe perf/trace support could be added eventually.

> diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
[]
> +/**
> + * fpga_mgr_status_write - Write fpga manager status
> + * @dev: Pointer to the device structure
> + * @attr: Pointer to the device attribute structure
> + * @buf: Pointer to the buffer location
> + * @count: Number of characters in @buf
> + *
> + * Returns the number of bytes copied to @buf, a negative error number otherwise
> + */
> +static ssize_t fpga_mgr_status_write(struct device *dev,
> +				     struct device_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	struct fpga_manager *mgr = dev_get_drvdata(dev);
> +	int ret;
> +
> +	if (test_and_set_bit_lock(FPGA_MGR_DEV_BUSY, &mgr->flags))
> +		return -EBUSY;
> +
> +	ret = strcmp(buf, "write_init");
> +	if (!ret) {
> +		ret = fpga_mgr_write_init(mgr);
> +		goto out;
> +	}
> +
> +	ret = strcmp(buf, "write_complete");
> +	if (!ret) {
> +		ret = fpga_mgr_write_complete(mgr);
> +		goto out;
> +	}
> +
> +	ret = strcmp(buf, "read_init");
> +	if (!ret) {
> +		ret = fpga_mgr_read_init(mgr);
> +		goto out;
> +	}
> +
> +	ret = strcmp(buf, "read_complete");
> +	if (!ret) {
> +		ret = fpga_mgr_read_complete(mgr);
> +		goto out;
> +	}
> +
> +	ret = -EINVAL;
> +out:
> +	clear_bit_unlock(FPGA_MGR_DEV_BUSY, &mgr->flags);
> +
> +	return ret ? : count;
> +}

I think this style is awkward and this would be
better written as:

	if (!strcmp(buf, "write_init"))
		ret = fpga_mgr_write_init(mgr);
	else if (!strcmp(buf, "write_complete"))
		ret = fpga_mgr_write_complete(mgr);
	else if (!strcmp(buf, "read_init"))
		ret = fpga_mgr_read_init(mgr);
	else if (!strcmp(buf, "read_complete"))
		ret = fpga_mgr_read_complete(mgr);
	else
		ret = -EINVAL;

	clear_bit_unlock(FPGA_MGR_DEV_BUSY, &mgr->flags);

	if (ret)
		return ret;

	return count;
}

Maybe use (strcmp(...) == 0) if you prefer that.
Both styles are commonly used in linux.

Probably all of the "return ret ?: count;" uses
would be more easily understood on 3 lines.


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