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libata: ahci_start_engine compliant to AHCI spec 

At the end of section 10.1 of AHCI spec (rev 1.3), it states

Software shall not set PxCMD.ST to 1 until it is determined that
a functoinal device is present on the port as determined by
PxTFD.STS.BSY=0, PxTFD.STS.DRQ=0 and PxSSTS.DET=3h

Even though most AHCI host controller works without this check,
specific controller will fail under this condition.

Signed-off-by: Jian Peng <jipeng2005@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
This commit is contained in:
Jian Peng 2011-04-22 23:58:10 -07:00 committed by Jeff Garzik
parent 792d37af35
commit 270dac35c2
1 changed files with 21 additions and 0 deletions
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21
drivers/ata/libahci.c
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@ -561,6 +561,27 @@ void ahci_start_engine(struct ata_port *ap)
{
void __iomem *port_mmio = ahci_port_base(ap);
u32 tmp;
u8 status;
status = readl(port_mmio + PORT_TFDATA) & 0xFF;
/*
* At end of section 10.1 of AHCI spec (rev 1.3), it states
* Software shall not set PxCMD.ST to 1 until it is determined
* that a functoinal device is present on the port as determined by
* PxTFD.STS.BSY=0, PxTFD.STS.DRQ=0 and PxSSTS.DET=3h
*
* Even though most AHCI host controllers work without this check,
* specific controller will fail under this condition
*/
if (status & (ATA_BUSY | ATA_DRQ))
return;
else {
ahci_scr_read(&ap->link, SCR_STATUS, &tmp);
if ((tmp & 0xf) != 0x3)
return;
}
/* start DMA */
tmp = readl(port_mmio + PORT_CMD);