Re: [PATCH v9 03/10] ata: zpodd: identify and init ZPODD devices

[Tejun Heo <tj@kernel.org>]

Hello, Aaron.

On Wed, Nov 14, 2012 at 09:32:27AM +0800, Aaron Lu wrote:
> > I don't think you're supposed to use dev->private_data from libata
> > core layer.  Just add a new field.  Nobody cares about adding 8 more
> > bytes to struct ata_device and spending 8 more bytes is way better
> > than muddying the ownership of ->private_data.
> 
> OK.
> And just out of curiosity, who's supposed to use device's private_data?
> I didn't find any user for ata_device's private_data in libata.

All the ->private_data fields are to be used by low level drivers
(ahci, ata_piix, pata_via...).  Given the twisted nature of ATA
devices, it's a bit surprising that no driver yet found a need for
ata_dev->private_data.  For most SATA controllers, port to device is
one to one so maybe ap->private_data is enough.

> > And this gets completely wrong.  What if the device supports DA and
> > low level driver makes use of ->private_data?
> 
> I didn't find any user of ata_device's private_data, so I used it for
> ZPODD. But if this is dangerous, I'll use a new field.

As there currently is no other user, it won't break anything but yeah
please add a properly typed and named field.

Thanks.

-- 
tejun