linux-kernel - Re: [PATCH] uio/pdrv

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Date:	Thu, 31 Mar 2011 19:03:21 +0200
From:	"Hans J. Koch" <hjk@...sjkoch.de>
To:	Michal Simek <monstr@...str.eu>
Cc:	Wolfram Sang <w.sang@...gutronix.de>,
	devicetree-discuss@...ts.ozlabs.org, grant.likely@...retlab.ca,
	john.williams@...alogix.com, linux-kernel@...r.kernel.org,
	hjk@...utronix.de, gregkh@...e.de
Subject: Re: [PATCH] uio/pdrv_genirq: Add OF support

On Thu, Mar 31, 2011 at 03:28:41PM +0200, Michal Simek wrote:
> >>+		uioinfo->name = pdev->dev.of_node->name;
> >>+		/* Use version for storing full IP name for identification */
> >>+		uioinfo->version = pdev->dev.of_node->full_name;
> >
> >I don't think this is apropriate, but will leave that to Hans.
> 
> I was thinking what to add and I choose full_name because I can read
> this value and identify which UIO is this device.
> I know that there should be version but there is no version string in DTS.

The purpose of uio_info->version is to give the userspace part of the driver
additional information. Kernel part and userspace part might be developed
independently, and there should be a chance for the userspace part to find
out if a certain feature is already supported by the kernel part without
having to do dirty kernel version checks.

So, uio_info->version is an information about the driver, not the hardware.

Example: You write a UIO driver for a chip you use in a project. You don't
need all the functionality of that chip. One year later you need additional
chip functionality, and it turns out that you have to do certain
initializations in the kernel part. Your new userspace will need the new
kernel driver, but there are lots of older kernels around in your customers
devices. In that case, your userspace part can simply check the version
string in sysfs and require at least your new version.

> 
> >
> >>+		/* Get IRQ for the device */
> >>+		rc = of_irq_to_resource(pdev->dev.of_node, 0, &r_irq);
> >>+		if (rc == NO_IRQ)
> >>+			dev_err(&pdev->dev, "no IRQ found\n");
> >
> >No error, I think. Sometimes just mmaping the registers is enough.
> 
> OK. Let's changed it to dev_info if you like.

The correct thing is to set uio_info->irq to UIO_IRQ_NONE.

Thanks,
Hans

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