iPod Classic: optimize UDMA timming for ATA drives

This patch optimizes UDMA timings to increase write transfer rate on
ATA bus, these transfers are clocked by HCLK, tDVS+tDVH is modified to
decrease Tcyctyp (typical write cycle period). This is not overclocking,
we meet the ATA standar, the settings used by OF are not well optimized
for each UDMA mode, we will never know but probably this was due some
documentation issue.

ATA_UDMA_TIME register is documented on s3c6400 datasheet, information
included in s5l8700 datasheet is wrong or not valid for s5l8702.

From ATA specs, (Minimum, Maximum) values in nanoseconds:

             UDMA 0      UDMA 1      UDMA 2      UDMA 3      UDMA 4
 tACKENV     (20, 70)    (20, 70)    (20, 70)    (20, 55)    (20, 55)
 tRP         (160, --)   (125, --)   (100, --)   (100, --)   (100, --)
 tSS         (50, --)    (50, --)    (50, --)    (50, --)    (50, --)
 tDVS        (70, --)    (48, --)    (31, --)    (20, --)    (6.7, --)
 tDVH        (6.2, --)   (6.2, --)   (6.2, --)   (6.2, --)   (6.2, --)
 tDVS+tDVH   (120, --)   (80, --)    (60, --)    (45, --)    (30, --)

 Tcyc = tDVS+tDVH
 WR[bytes/s] = 1/Tcyc[s] * 2[bytes]

On Classic (boosted):
 HClk = 108 MHz. -> T = ~9.26 ns.

Old values (used by OF):
 UDMA  ATA_UDMA_TIME  tACK  tRP    tSS   tDVS  tDVH  Tcyc   WR(MB/s)
 0     0x5071152      27.8  166.7  55.6  74.1  55.6  129.7  15.4
 1     0x3050a52      27.8  101.8  55.6  55.6  37     92.6  21.6
 2     0x3030a52      27.8  101.8  55.6  37    37     74    27
 3     0x2020a52      27.8  101.8  55.6  27.8  27.8   55.6  36
 4     0x2010a52      27.8  101.8  55.6  18.5  27.8   46.3  43.2

New values:
 UDMA  ATA_UDMA_TIME  tACK  tRP    tSS   tDVS  tDVH  Tcyc   WR(MB/s)
 0     0x4071152      27.8  166.7  55.6  74.1  46.3  120.4  16.6
 1     0x2050d52      27.8  129.6  55.6  55.6  27.8   83.4  24
 2     0x2030a52      27.8  101.8  55.6  37    27.8   64.8  30.9
 3     0x1020a52      27.8  101.8  55.6  27.8  18.5   46.3  43.2
 4     0x1010a52      27.8  101.8  55.6  18.5  18.5   37    54

To verify that the settings are correct, a write-to-cache test was
performed using emCORE, the measured transfer rate (WRm) is compared
against the theoric transfer rate (WR) at 108 Mhz for the old and
the new UDMA4 settings (iPod 160, HDD Toshiba MK1634GAL):

 UDMA  ATA_UDMA_TIME  Tcyc(ns)  WR(MB/s)  WRm(MB/s)  RDm(MB/s)
 4     0x2010a52      46.3      43.2      42.9       59.8
 4     0x1010a52      37        54        53.5       59.8

Notes:
 - The new UDMA4 settings increases ~25% the ATA transfer rate for
   cached-writes. The real HDD write speed is limited by the internal
   transfer rate (depends on cilinder, for the MK1634GAL it is 276 to
   573 Mbits/s). Sequential write benchmark using diskdump on USB are
   ~8% faster.
 - Read transfers are clocked by the device, it depends on UDMA mode
   selected and are not affected by HClk or ATA_UDMA_TIME settings.
   Read-from-cache tests results (RDm) using HClk=108 and HClk=54 for
   UDMA4 are 59.8 MB/s on MK1634GAL.
 - Minimum HClk is limited by tACKENV specs, using current settings
   it is 54 MHz for UDMA4,UDMA3 and 43 MHz for UDMA2,UDMA1,UDMA0.

Change-Id: I61d67060410752518a59e1ff08072b21747ca997

0 files changed, 0 insertions, 0 deletions