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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>
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@ -561,6 +561,27 @@ 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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u8 status;
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status = readl(port_mmio + PORT_TFDATA) & 0xFF;
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/*
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* At end of section 10.1 of AHCI spec (rev 1.3), it states
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* Software shall not set PxCMD.ST to 1 until it is determined
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* that a functoinal device is present on the port as determined by
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* PxTFD.STS.BSY=0, PxTFD.STS.DRQ=0 and PxSSTS.DET=3h
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*
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* Even though most AHCI host controllers work without this check,
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* specific controller will fail under this condition
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*/
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if (status & (ATA_BUSY | ATA_DRQ))
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return;
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else {
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ahci_scr_read(&ap->link, SCR_STATUS, &tmp);
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if ((tmp & 0xf) != 0x3)
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return;
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}
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/* start DMA */
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tmp = readl(port_mmio + PORT_CMD);
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