diff options
Diffstat (limited to 'drivers/ata')
| -rw-r--r-- | drivers/ata/ahci_sunxi.c | 47 |
1 files changed, 45 insertions, 2 deletions
diff --git a/drivers/ata/ahci_sunxi.c b/drivers/ata/ahci_sunxi.c index 4100e904376b..cb69b737cb49 100644 --- a/drivers/ata/ahci_sunxi.c +++ b/drivers/ata/ahci_sunxi.c @@ -149,8 +149,51 @@ static void ahci_sunxi_start_engine(struct ata_port *ap) void __iomem *port_mmio = ahci_port_base(ap); struct ahci_host_priv *hpriv = ap->host->private_data; - /* Setup DMA before DMA start */ - sunxi_clrsetbits(hpriv->mmio + AHCI_P0DMACR, 0x0000ff00, 0x00004400); + /* Setup DMA before DMA start + * + * NOTE: A similar SoC with SATA/AHCI by Texas Instruments documents + * this Vendor Specific Port (P0DMACR, aka PxDMACR) in its + * User's Guide document (TMS320C674x/OMAP-L1x Processor + * Serial ATA (SATA) Controller, Literature Number: SPRUGJ8C, + * March 2011, Chapter 4.33 Port DMA Control Register (P0DMACR), + * p.68, https://www.ti.com/lit/ug/sprugj8c/sprugj8c.pdf) + * as equivalent to the following struct: + * + * struct AHCI_P0DMACR_t + * { + * unsigned TXTS : 4; + * unsigned RXTS : 4; + * unsigned TXABL : 4; + * unsigned RXABL : 4; + * unsigned Reserved : 16; + * }; + * + * TXTS: Transmit Transaction Size (TX_TRANSACTION_SIZE). + * This field defines the DMA transaction size in DWORDs for + * transmit (system bus read, device write) operation. [...] + * + * RXTS: Receive Transaction Size (RX_TRANSACTION_SIZE). + * This field defines the Port DMA transaction size in DWORDs + * for receive (system bus write, device read) operation. [...] + * + * TXABL: Transmit Burst Limit. + * This field allows software to limit the VBUSP master read + * burst size. [...] + * + * RXABL: Receive Burst Limit. + * Allows software to limit the VBUSP master write burst + * size. [...] + * + * Reserved: Reserved. + * + * + * NOTE: According to the above document, the following alternative + * to the code below could perhaps be a better option + * (or preparation) for possible further improvements later: + * sunxi_clrsetbits(hpriv->mmio + AHCI_P0DMACR, 0x0000ffff, + * 0x00000033); + */ + sunxi_clrsetbits(hpriv->mmio + AHCI_P0DMACR, 0x0000ffff, 0x00004433); /* Start DMA */ sunxi_setbits(port_mmio + PORT_CMD, PORT_CMD_START); |