By "Parallel ATA" we mean all the ATA/IDE controllers and drives that we have been using for years before SATA. Almost from the start, one of the objectives of some kernel hackers was to replace the IDE drivers available in drivers/ide (everything under the "Device drivers -> ATA/ATAPI/MFM/RLL support" configuration menu) with a reimplementation on top of libata (i.e.: the "SATA layer"). Drivers/ide suffers from many ugly and obscure problems, and re-implementing it on top of libata has been much easier than fixing the unfixable drivers/ide mess - most of the porting work has been done by Alan Cox (a consequence of this PATA merge is that libata and all its SATA drivers have also been moved from drivers/scsi (available in the "Device drivers -> SCSI device support -> SCSI low-level drivers" submenu) to drivers/ata (now "Device drivers -> Serial ATA (prod) and Parallel ATA (experimental) drivers"), and all the CONFIG_SCSI_FOOBAR options for the individual SATA drivers have been changed to CONFIG_FOOBAR, so this means you may need to reconfigure your SATA configuration options)
This means 2.6.19 may have two drivers for your PATA-based device: The old IDE driver under "Device drivers -> ATA/ATAPI/MFM/RLL support" and an alternative driver under "Device drivers -> Serial ATA (prod) and Parallel ATA (experimental) drivers" (along with the rest of the SATA drivers)
What one must you choose? Well, the safe option is using the old driver: The old drivers will continue working just as they did before. There'll be no changes if you continue using the old drivers.
What do the new libata-based PATA drivers offer to you?
- First of all, because they're libata-based and libata is a well engineered and sane infrastructure, the drivers have much better quality, they're cleaner, they've much better error handling (much better behaviour when one of your drives dies suddenly or finds broken sectors), and they don't have some of the known design issues that the old drivers have (this is why people did all the work to move away from drivers/ide, they didn't do it just for fun)
- Because they're newer, there are more bugs. For this release, they're "experimental". If you want to be safe, use the old drivers.
- Really. There is a risk that the new drivers won't work for you, or may harm your data (unlikely, but not impossible). If you want to be safe, use the old drivers.
- They support some chipsets not supported by drivers/ide. The cleaner design of libata allows for easier driver development and maintenance. In some cases it supports features that the old driver doesn't, for the same reasons.
- Some IDE controllers are not supported or they aren't fully supported. Some of them because not all the IDE drivers have been ported to libata, but others because they're old and undocumented or because the libata PATA layer still doesn't support some of their features. There's no support for certain old serialized devices, for prehistoric CMD640 controllers or for host-protected-area yet.
- Drives appear as /dev/sda, /dev/sr0, the old devices names won't work. You will need to change your boot parameters and your /etc/fstab parameters in order to get a working system with the new drivers. Again, this only happens if you use the new drivers, the old drivers continue working as they did before.
Eventually, the new libata-based PATA drivers will get more stable, so the old drivers in drivers/ide may get deleted as the new drivers fulfill all needs of the IDE users and become feature-complete. But this certainly won't happen anytime soon. No old drivers will be deleted if there's not a working libata-based replacement. You can read the latest status report written by Alan Cox. It'd certainly be useful if you could give it a try and report back how well it works to
linux-kernel@vger.kernel.org or bugzilla.kernel.org - even if it works fine, it'll be useful to know what systems do work (be sure to include the necessary information mentioned in the previous status report). (libata PATA code)
It is probably worth reiterating that if you have SATA drives, and you do a make oldconfig from a 2.6.18 or previous kernel, your system will not boot unless you specifically go in and enable the new SATA subsystem, and the driver for your controller.
