vortex86 SIS550 Minit-5250E瘦客户机，
使用CF卡启动，显示不支持DMA。
搜索得新内核已基本不再使用ide=nodma参数了，查到这篇文章：“Debian下关闭CF卡的DMA模式”
在grub的启动参数中了一条 “libata.dma=0”就关闭DMA了。
原来的dmesg可以看到内核不断尝试DMA方式，直到最后PIO方式才能正确访问。
[ 10.687047] ata1.00: configured for UDMA/33
[ 10.689746] scsi 0:0:0:0: Direct-Access ATA ELITE PRO CF CAR 2009 PQ: 0 ANSI: 5
[ 12.128626] sd 0:0:0:0: [sda] 15662304 512-byte logical blocks: (8.01 GB/7.46 GiB)
[ 12.138999] sd 0:0:0:0: [sda] Write Protect is off
[ 12.139144] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
[ 12.147593] sd 0:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[ 42.848609] ata1: lost interrupt (Status 0x50)
[ 42.848830] ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[ 42.848609] ata1: lost interrupt (Status 0x50)
[ 42.848830] ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[ 42.848967] ata1.00: failed command: READ DMA
[ 42.849118] ata1.00: cmd c8/00:08:00:00:00/00:00:00:00:00/e0 tag 0 dma 4096 in
[ 42.849138] res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
[ 42.849327] ata1.00: status: { DRDY }
[ 42.849581] ata1: soft resetting link
[ 43.028910] ata1.00: configured for UDMA/33
[ 43.029081] ata1.00: device reported invalid CHS sector 0
[ 43.029317] ata1: EH complete
[ 73.826377] ata1: lost interrupt (Status 0x50)
[ 73.826604] ata1.00: limiting speed to UDMA/25:PIO4
[ 73.826748] ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[ 73.826884] ata1.00: failed command: READ DMA
[ 73.827041] ata1.00: cmd c8/00:08:00:00:00/00:00:00:00:00/e0 tag 0 dma 4096 in
[ 73.827060] res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
[ 73.828159] ata1.00: status: { DRDY }
[ 73.828425] ata1: soft resetting link
[ 74.014659] ata1.00: configured for UDMA/25
[ 74.014826] ata1.00: device reported invalid CHS sector 0
[ 74.015062] ata1: EH complete
[ 104.932150] ata1: lost interrupt (Status 0x50)
[ 104.932376] ata1.00: limiting speed to PIO4
[ 104.932518] ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[ 104.932653] ata1.00: failed command: READ DMA
[ 104.932811] ata1.00: cmd c8/00:08:00:00:00/00:00:00:00:00/e0 tag 0 dma 4096 in
[ 104.932831] res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
[ 104.933024] ata1.00: status: { DRDY }
[ 104.933285] ata1: soft resetting link
[ 105.112426] ata1.00: configured for PIO4
[ 105.112594] ata1.00: device reported invalid CHS sector 0
[ 105.112828] ata1: EH complete
[ 105.118050] sda: sda1 sda2 < sda5 > sda3
[ 105.146093] sd 0:0:0:0: [sda] Attached SCSI disk
[ 105.192368] sda: detected capacity change from 0 to 8019099648
[ 105.335586] sd 0:0:0:0: Attached scsi generic sg0 type 0