[libata] sata_sx4, sata_via: minor documentation updates

sata_sx4:
- describe overall driver theory of operation
- add a few constants that will be used in the future

sata_via:
- remove mention of an old-EH function that is going away

Signed-off-by: Jeff Garzik <jeff@garzik.org>

diff --git a/drivers/ata/sata_sx4.c b/drivers/ata/sata_sx4.c
index ff0a78dc8b86e38db52aa57006d25635d6478a50..3d83ee273388d4ff56ea322c25d8a0b3e2e424e8 100644 (file)
--- a/drivers/ata/sata_sx4.c
+++ b/drivers/ata/sata_sx4.c
@@ -30,6 +30,54 @@
  *
  */
 
+/*
+       Theory of operation
+       -------------------
+
+       The SX4 (PDC20621) chip features a single Host DMA (HDMA) copy
+       engine, DIMM memory, and four ATA engines (one per SATA port).
+       Data is copied to/from DIMM memory by the HDMA engine, before
+       handing off to one (or more) of the ATA engines.  The ATA
+       engines operate solely on DIMM memory.
+
+       The SX4 behaves like a PATA chip, with no SATA controls or
+       knowledge whatsoever, leading to the presumption that
+       PATA<->SATA bridges exist on SX4 boards, external to the
+       PDC20621 chip itself.
+
+       The chip is quite capable, supporting an XOR engine and linked
+       hardware commands (permits a string to transactions to be
+       submitted and waited-on as a single unit), and an optional
+       microprocessor.
+
+       The limiting factor is largely software.  This Linux driver was
+       written to multiplex the single HDMA engine to copy disk
+       transactions into a fixed DIMM memory space, from where an ATA
+       engine takes over.  As a result, each WRITE looks like this:
+
+               submit HDMA packet to hardware
+               hardware copies data from system memory to DIMM
+               hardware raises interrupt
+
+               submit ATA packet to hardware
+               hardware executes ATA WRITE command, w/ data in DIMM
+               hardware raises interrupt
+       
+       and each READ looks like this:
+
+               submit ATA packet to hardware
+               hardware executes ATA READ command, w/ data in DIMM
+               hardware raises interrupt
+       
+               submit HDMA packet to hardware
+               hardware copies data from DIMM to system memory
+               hardware raises interrupt
+
+       This is a very slow, lock-step way of doing things that can
+       certainly be improved by motivated kernel hackers.
+
+ */
+
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/pci.h>
@@ -58,6 +106,8 @@ enum {
        PDC_INT_SEQMASK         = 0x40, /* Mask of asserted SEQ INTs */
        PDC_HDMA_CTLSTAT        = 0x12C, /* Host DMA control / status */
 
+       PDC_CTLSTAT             = 0x60, /* IDEn control / status */
+
        PDC_20621_SEQCTL        = 0x400,
        PDC_20621_SEQMASK       = 0x480,
        PDC_20621_GENERAL_CTL   = 0x484,
@@ -89,6 +139,7 @@ enum {
 
        PDC_MASK_INT            = (1 << 10), /* HDMA/ATA mask int */
        PDC_RESET               = (1 << 11), /* HDMA/ATA reset */
+       PDC_DMA_ENABLE          = (1 << 7),  /* DMA start/stop */
 
        PDC_MAX_HDMA            = 32,
        PDC_HDMA_Q_MASK         = (PDC_MAX_HDMA - 1),

diff --git a/drivers/ata/sata_via.c b/drivers/ata/sata_via.c
index e8b90e7b42ddcfa56e5253941bc33532258aeed0..e816965ef4f188cfe02e47fd45df96da6a31297a 100644 (file)
--- a/drivers/ata/sata_via.c
+++ b/drivers/ata/sata_via.c
@@ -303,9 +303,7 @@ static int vt6420_prereset(struct ata_port *ap, unsigned long deadline)
        if (!(ap->pflags & ATA_PFLAG_LOADING))
                goto skip_scr;
 
-       /* Resume phy.  This is the old resume sequence from
-        * __sata_phy_reset().
-        */
+       /* Resume phy.  This is the old SATA resume sequence */
        svia_scr_write(ap, SCR_CONTROL, 0x300);
        svia_scr_read(ap, SCR_CONTROL); /* flush */