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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: Matthew Garrett <mjg@redhat.com> Cc: Kristen Carlson Accardi <kristen.c.accardi@intel.com> Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
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1 changed files with 18 additions and 0 deletions
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@ -437,11 +437,29 @@ static int ahci_scr_write(struct ata_link *link, unsigned int sc_reg, u32 val)
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return -EINVAL;
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}
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static int ahci_is_device_present(void __iomem *port_mmio)
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{
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u8 status = readl(port_mmio + PORT_TFDATA) & 0xff;
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/* Make sure PxTFD.STS.BSY and PxTFD.STS.DRQ are 0 */
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if (status & (ATA_BUSY | ATA_DRQ))
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return 0;
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/* Make sure PxSSTS.DET is 3h */
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status = readl(port_mmio + PORT_SCR_STAT) & 0xf;
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if (status != 3)
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return 0;
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return 1;
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}
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void ahci_start_engine(struct ata_port *ap)
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{
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void __iomem *port_mmio = ahci_port_base(ap);
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u32 tmp;
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if (!ahci_is_device_present(port_mmio))
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return;
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/* start DMA */
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tmp = readl(port_mmio + PORT_CMD);
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tmp |= PORT_CMD_START;
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