According to section 10.3.1 of the AHCI spec, PxCMD.ST must not be set
unless there's a device attached. Following this saves us a measurable
quantity of power and does not impair hotplug support. Based on a patch
by Kristen Carlson Accardi.
Signed-off-by: Matthew Garrett <mjg@xxxxxxxxxx>
Cc: Kristen Carlson Accardi <kristen.c.accardi@xxxxxxxxx>
---
drivers/ata/ahci.c | 19 +++++++++++++++++++
1 files changed, 19 insertions(+), 0 deletions(-)
diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 6bd930b..ff08317 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -1016,11 +1016,30 @@ static int ahci_scr_write(struct ata_link *link, unsigned int sc_reg, u32 val)
return -EINVAL;
}
+static int ahci_is_device_present(struct ata_port *ap)
+{
+ void __iomem *port_mmio = ahci_port_base(ap);
+ u8 status = readl(port_mmio + PORT_TFDATA) & 0xff;
+
+ /* Make sure PxTFD.STS.BSY and PxTFD.STS.DRQ are 0 */
+ if (status & (ATA_BUSY | ATA_DRQ))
+ return 0;
+
+ /* Make sure PxSSTS.DET is 3h */
+ status = readl(port_mmio + PORT_SCR_STAT) & 0xf;
+ if (status != 3)
+ return 0;
+ return 1;
+}
+
static void ahci_start_engine(struct ata_port *ap)
{
void __iomem *port_mmio = ahci_port_base(ap);
u32 tmp;
+ if (!ahci_is_device_present(ap))
+ return;
+
/* start DMA */
tmp = readl(port_mmio + PORT_CMD);
tmp |= PORT_CMD_START;
--
1.6.6.1
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