Merge tag 'hwlock-v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/andersson...

[linux-2.6-microblaze.git] / drivers / ata / ahci_sunxi.c

diff --git a/drivers/ata/ahci_sunxi.c b/drivers/ata/ahci_sunxi.c
index 4100e90..cb69b73 100644 (file)
--- 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);