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Commit 96d60303 authored by Matthew Garrett's avatar Matthew Garrett Committed by Jeff Garzik
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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: default avatarMatthew Garrett <mjg@redhat.com>
Cc: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: default avatarJeff Garzik <jgarzik@redhat.com>
parent 1c2a49f6

drivers/ata/libahci.c

+18 −0
Original line number Diff line number Diff line
@@ -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;