Fix a number of issues with the DMA support code:
- driver claims support for all SW/MW DMA modes while supporting only MWDMA2;
- ide_dma_check() method tries to enable DMA on the "known good" drives which
don't support MWDMA2;
- ide_dma_on() method upon failure to set drive to MWDMA2 re-tunes already
tuned PIO mode and calls ide_dma_off() method instead of returning error;
- ide_dma_off() method sets drive->current_speed while it doesn't actually
change (only the PIO timings are re-loaded into the chip's registers);
- init_hwif() method forcibly sets/resets both "drive DMA capable" bits while
this is properly handled by ide_dma_{on,off}() methods being called later...
Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
ea266ba159