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authorMatthew Garrett <mjg@redhat.com>2010-03-28 00:37:21 -0400
committerJeff Garzik <jgarzik@redhat.com>2010-05-14 17:08:01 -0400
commit96d60303fd3336893a93565d58c4f1805a327061 (patch)
treee6534dabeceb4a0a0b511c17dbffe47639fff0ac
parent1c2a49f61785ebbcbfb481a2aab659020f0457f7 (diff)
downloadop-kernel-dev-96d60303fd3336893a93565d58c4f1805a327061.zip
op-kernel-dev-96d60303fd3336893a93565d58c4f1805a327061.tar.gz
ahci: Turn off DMA engines when there's no device attached
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@redhat.com> Cc: Kristen Carlson Accardi <kristen.c.accardi@intel.com> Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
-rw-r--r--drivers/ata/libahci.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 38e1b4e..3f586ec 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -437,11 +437,29 @@ static int ahci_scr_write(struct ata_link *link, unsigned int sc_reg, u32 val)
return -EINVAL;
}
+static int ahci_is_device_present(void __iomem *port_mmio)
+{
+ 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;
+}
+
void ahci_start_engine(struct ata_port *ap)
{
void __iomem *port_mmio = ahci_port_base(ap);
u32 tmp;
+ if (!ahci_is_device_present(port_mmio))
+ return;
+
/* start DMA */
tmp = readl(port_mmio + PORT_CMD);
tmp |= PORT_CMD_START;
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