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

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Date:	Thu, 31 Mar 2011 13:48:32 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	"Hans J. Koch" <hjk@...sjkoch.de>
Cc:	Michal Simek <monstr@...str.eu>,
	Wolfram Sang <w.sang@...gutronix.de>,
	devicetree-discuss@...ts.ozlabs.org, 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 1:23 PM, Hans J. Koch <hjk@...sjkoch.de> wrote:
> On Thu, Mar 31, 2011 at 07:57:47PM +0200, Michal Simek wrote:
>> Hans J. Koch wrote:
>> >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.
>>
>> I understand reasons but this information is not in device tree and
>> it must be setup.
>> Grant suggested compatible string but it is not the best option too.
>
> In uio_pdrv_genirq, uio_info->version is hardcoded in platform data. Hardware
> initialization can also take place in the same platform specific file, which
> is common practice on archs like ARM. Therefore, a driver specific versioning
> can make sense for UIO, even if the driver code itself doesn't change.
>
> If you have no equivalent for that in device tree, you should create a new
> generic driver (uio_of_genirq?) that simply doesn't support this kind of
> versioning.

I'd avoid that.  Current trend is to move away from separate
of-specific data because the driver is essentially identical other
than the data source being different (platform_data vs. a device node
pointer).

g.
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