* disk/ata.c (grub_ata_regget): Change return type to
`grub_uint8_t'.
(grub_ata_regget2): Likewise.
(grub_ata_wait_status): New function.
(grub_ata_wait_busy): Removed function, updated all users to use
`grub_ata_wait_status'.
(grub_ata_wait_drq): Likewise.
(grub_ata_cmd): New function.
(grub_ata_pio_read): Change return type to `grub_uint8_t'. Add
error handling.
(grub_ata_pio_write): Add error handling.
(grub_atapi_identify): Likewise.
(grub_atapi_packet): Use `grub_ata_cmd' and improve error
handling.
(grub_ata_identify): Use `grub_ata_cmd' and improve error
handling. Actually use the detected registers. Reorder the
detection logic such that it is easier to read.
(grub_ata_pciinit): Do not assign the same ID to each controller.
(grub_ata_setaddress): Use `grub_ata_cmd' and improve error
handling.
(grub_atapi_readsector): Check the result of `grub_ata_pio_read'.
* include/grub/err.h (grub_err_t): Add `GRUB_ERR_TIMEOUT'.
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