For unknown reason, kernel set the obsolete bit in both device control register and device register, and never used.
Device Control Register
Device/Head Register
include/linux/ata.h
ATA_DEVICE_OBS = (1 << 7) | (1 << 5), /* obs bits in dev reg */
ATA_DEVCTL_OBS = (1 << 3), /* obsolete bit in devctl reg */
ATA_BUSY = (1 << 7), /* BSY status bit */
drivers/ata/libata-core.c
/**
* ata_port_alloc - allocate and initialize basic ATA port resources
* @host: ATA host this allocated port belongs to
*
* Allocate and initialize basic ATA port resources.
*
* RETURNS:
* Allocate ATA port on success, NULL on failure.
*
* LOCKING:
* Inherited from calling layer (may sleep).
*/
struct ata_port *ata_port_alloc(struct ata_host *host)
{
struct ata_port *ap;
DPRINTK("ENTER\n");
ap = kzalloc(sizeof(*ap), GFP_KERNEL);
if (!ap)
return NULL;
ap->pflags |= ATA_PFLAG_INITIALIZING;
ap->lock = &host->lock;
ap->flags = ATA_FLAG_DISABLED;
ap->print_id = -1;
ap->ctl = ATA_DEVCTL_OBS;
ap->host = host;
include/linux/libata.h
static inline void ata_tf_init(struct ata_device *dev, struct ata_taskfile *tf)
{
memset(tf, 0, sizeof(*tf));
tf->ctl = dev->link->ap->ctl;
if (dev->devno == 0)
tf->device = ATA_DEVICE_OBS;
else
tf->device = ATA_DEVICE_OBS | ATA_DEV1;
}
drivers/ata/libata-core.c
/**
* ata_tf_to_fis - Convert ATA taskfile to SATA FIS structure
* @tf: Taskfile to convert
* @pmp: Port multiplier port
* @is_cmd: This FIS is for command
* @fis: Buffer into which data will output
*
* Converts a standard ATA taskfile to a Serial ATA
* FIS structure (Register - Host to Device).
*
* LOCKING:
* Inherited from caller.
*/
void ata_tf_to_fis(const struct ata_taskfile *tf, u8 pmp, int is_cmd, u8 *fis)
{
fis[0] = 0x27; /* Register - Host to Device FIS */
fis[1] = pmp & 0xf; /* Port multiplier number*/
if (is_cmd)
fis[1] |= (1 << 7); /* bit 7 indicates Command FIS */
fis[2] = tf->command;
fis[3] = tf->feature;
fis[4] = tf->lbal;
fis[5] = tf->lbam;
fis[6] = tf->lbah;
fis[7] = tf->device;
fis[8] = tf->hob_lbal;
fis[9] = tf->hob_lbam;
fis[10] = tf->hob_lbah;
fis[11] = tf->hob_feature;
fis[12] = tf->nsect;
fis[13] = tf->hob_nsect;
fis[14] = 0;
fis[15] = tf->ctl;
fis[16] = 0;
fis[17] = 0;
fis[18] = 0;
fis[19] = 0;
}
http://www.nntpnews.net/f3455/re-patch-09-18-ide-add-set_irq-method-3125152/
http://www.spinics.net/lists/linux-ide/msg26882.html
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