Re: [rfc][patch] ide: fix unneeded LBA48 taskfile registers access

[Tejun Heo <htejun@gmail.com>]

Hello, Bartlomiej.

Bartlomiej Zolnierkiewicz wrote:
> [ against ide-dev-2.6 tree, boot tested on LBA48 drive ]
> 
> This small patch fixes unneeded writes/reads to LBA48 taskfile registers
> on LBA48 capable disks for following cases:
> 
> * Power Management requests
>   (WIN_FLUSH_CACHE[_EXT], WIN_STANDBYNOW1, WIN_IDLEIMMEDIATE commands)
> * special commands (WIN_SPECIFY, WIN_RESTORE, WIN_SETMULT)
> * Host Protected Area support (WIN_READ_NATIVE_MAX, WIN_SET_MAX)
> * /proc/ide/ SMART support (WIN_SMART with SMART_ENABLE,
>   SMART_READ_VALUES and SMART_READ_THRESHOLDS subcommands)
> * write cache enabling/disabling in ide-disk
>   (WIN_SETFEATURES with SETFEATURES_{EN,DIS}_WCACHE)
> * write cache flushing in ide-disk (WIN_FLUSH_CACHE[_EXT])
> * acoustic management in ide-disk
>   (WIN_SETFEATURES with SETFEATURES_{EN,DIS}_AAM)
> * door (un)locking in ide-disk (WIN_DOORLOCK, WIN_DOORUNLOCK)
> * /proc/ide/hd?/identify support (WIN_IDENTIFY)
> 
> Patch adds 'unsinged long flags' to ide_task_t and uses ATA_TFLAG_LBA48
> flag (from <linux/ata.h>) to indicate need of accessing LBA48 taskfile
> registers.

  ide_task_t already has fields to enable/disable writing/reading of 
taskfile and hob registers (tf_in_flags and tf_out_flags).  How about 
adding the following two helpers.

static inline ide_init_task[_std](ide_task_t *task)
{
	memset(task, 0, sizeof(*task));
	task->tf_out_flags = IDE_TASKFILE_STD_OUT_FLAGS;
	task->tf_in_flags = IDE_TASKFILE_STD_IN_FLAGS;
}

static inline ide_init_task_lba48(ide_task_t *task)
{
	memset(task, 0, sizeof(*task));
	task->tf_out_flags = IDE_TASKFILE_STD_OUT_FLAGS
			| (IDE_HOB_STD_OUT_FLAGS << 8);
	task->tf_in_flags = IDE_TASKFILE_STD_IN_FLAGS
			| (IDE_HOB_STD_IN_FLAGS << 8);
}

  And, when writing taskfile,

if (task->tf_out_flags & 0xf == IDE_TASKFILE_STD_OUT_FLAGS) {
	/* Write taskfile regs without testing flags */
} else {
	/* Flagged taskfile */
}

if (task->tf_out_flags & 0xf0 == IDE_TASKFILE_HOB_OUT_FLAGS) {
	/* Write hob regs without testing flags */
} else {
	/* Flagged hob */
}

  And, when reading taskfile back,

if (task->tf_in_flags & 0xf0) {
	/* Read all hob regs */
}

/* Read all taskfile regs */

  And, we need to check if any of in/out flags is zero in ioctl 
functions and set STD flags appropriately.  So, basically, in kernel, 
tf_{in|out}_flags == 0 now means 0, not default.

  By doing like above,

  1. Virtually the same effect
  2. No need to add new field to ide_task_t
  3. Cleaner semantics (ATA_TFLAG_LBA48 and tf_{in|out}_flags carry
     duplicate information.)

  Thanks.

-- 
tejun