Re: [PATCH 1/9] drivers/video: fsl-diu-fb: fix some ioctls

Florian Tobias Schandinat wrote:

On 09/28/2011 09:19 PM, Timur Tabi wrote:

quoted

Use the _IOx macros to define the ioctl commands, instead of hard-coded
numbers.  Unfortunately, the original definitions of MFB_SET_PIXFMT and
MFB_GET_PIXFMT used the wrong value for the size, so this will break
binary compatibility with older applications.

Don't break compatibility without the need to do so. Ask yourself whether using
those macros is really worth it. If the answer is yes, at least give userspace a
grace period, some kernel versions where both values work. For example you could
rename the old numerical ones to MFB_SET_PIXFMT_OLD and then add a compatibility
IOCTL, for example like this

case MFB_SET_PIXFMT_OLD:
	/* you could add a warning message here */
case MFB_SET_PIXFMT:
	...

Ok, I can do that.

Not much work and you could delete the compatibility stuff in a year or two but
it would it make much easier for users to upgrade.

I don't know your driver, can int be only 32 bit on all plattforms where it can
be used or is this another thing where compatibility can break?

We have 64-bit processors, but currently none of them have any multimedia
support.  That might change one day, and I'd rather the drivers be 64-bit clean
before we announce any such parts.  There are other places in the driver that
break on 64-bit, and I will fix those as well (just not today).

-- 
Timur Tabi
Linux kernel developer at Freescale