Re: [PATCH] (pata-2.6 fix queue) cmd64x: remove broken SW/MW DMA support

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

On Friday 16 February 2007 16:00, Sergei Shtylyov wrote:
> Hello.
> 
> Bartlomiej Zolnierkiewicz wrote:
> 
> >>Mikael Pettersson wrote:
> 
> >>>>>Remove the bogus code pretending to set SW/MW DMA timings -- I wonder whether
> >>>>>its author really thought that he could achieve that wrtiting to BMIDE status
> >>>>>registers?  Stop fiddling with the DMA capable bits in the speedproc() -- they
> >>>>>do not enable DMA, and are properly dealt with by the dma_host_{on,off} methods;
> >>>>>also, get rid of the duplicate reads/writes of UDIDETCRx registers, and do some
> >>>>>coding style and whitespace changes while at it...
> 
> >>>>>Unfortunately, fixing the SW/MW DMA support would requre a major driver rewrite
> >>>>>along with some more fixing, so I'm putting it off...
> 
> >>>>>Warning: this has been compile-tested only.
> 
> >>>>Worked fine on my SPARC Ultra5.
> 
> >>>Correction: I was only looking for absence of errors when testing
> >>>this patch. However, later I found that this patch (version 1.42
> >>>of cmd64x.c) disabled DMA on my CMD646, dropping performance to
> >>>1/4th (from about 13MB/s to about 3.5MB/s according to hdparm -Tt).
> 
> >>    That was expected behavior.
> 
> >>>Here's the relevant kernel messages from before this patch:
> 
> >>>ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
> >>>CMD646: IDE controller at PCI slot 0000:01:03.0
> >>>CMD646: chipset revision 3
> >>>CMD646: chipset revision 0x03, MultiWord DMA Force Limited
> 
> >>    The driver never supported UltraDMA on this revision, as indicated by that 
> >>message.
> 
> >>>CMD646: 100% native mode on irq 14
> >>>    ide0: BM-DMA at 0x1fe02c00020-0x1fe02c00027, BIOS settings: hda:pio, hdb:pio
> >>>    ide1: BM-DMA at 0x1fe02c00028-0x1fe02c0002f, BIOS settings: hdc:pio, hdd:pio
> >>>Probing IDE interface ide0...
> >>>hda: ST320420A, ATA DISK drive
> >>>ide0 at 0x1fe02c00000-0x1fe02c00007,0x1fe02c0000a on irq 14
> >>>Probing IDE interface ide1...
> >>>hdc: CRD-8483B, ATAPI CD/DVD-ROM drive
> >>>ide1 at 0x1fe02c00010-0x1fe02c00017,0x1fe02c0001a on irq 14 (shared with ide0)
> >>>hda: max request size: 128KiB
> >>>hda: 39851760 sectors (20404 MB) w/2048KiB Cache, CHS=39535/16/63, (U)DMA
> >>>hda: cache flushes not supported
> >>> hda: hda1 hda2 hda3 hda4 hda5
> 
> >>>With the patch the kernel messages are the same, except for the
> >>>3rd last line which becomes:
> 
> >>>hda: 39851760 sectors (20404 MB) w/2048KiB Cache, CHS=39535/16/63
> 
> >>>i.e., the (U)DMA indicator is gone.
> 
> >>>Please revert this until the regression is fixed.
> 
> >>    The intent of the patch was exactly to *remove* broken DMA support until 
> >>it's fixed (which requires more work).  It only worked by chance -- because 
> >>MWDMA2 timings are the same as of PIO4.  Have patience please.
> 
> > It only worked by chance but it _worked_, especially for the usual case,
> > MWDMA2/PIO4 == all newer drives (despite writing 0x10 reserved bit of
> > BMIDESR0/1 for the master devices).  I think I'll remove the patch for now.
> 
>     Then I will protest. :-) This was *not* fixable all at once. And removing 
> it just because some users happen to have the *known buggy* (and so reduced to 
> MWDMA only) chips is a wrong thing to do.

OK, I'm not removing it but it needs (rather urgent) fixing.

> > To fix SWDMA/MWDMA properly isn't it enough to just call cmd64x_tune_pio()
> > from cmd64x_tune_chipset() to tune the corresponding PIO mode?
> 
>     No, that wouldn't be a clean fix, just a kind of workaround -- it will 
> also change the address setup times (which is not quite desirable).  I can 

I see, how about:

* splitting off setup timing programming from program_drive_counts()
  into separate function (setup timing is programmed into separate register)

* pushing ide_get_best_pio_mode() call to higher layers
  [ cmd64x_tune_driver() only, it is not needed in cmd64x_tune_chipset() ]

* calling new function setting setup timing from cmd64x_tune_drive()
  and cmd64x_tune_chipset() (here for PIO modes only)

* calling cmd64x_tune_pio() fro SWDMA/MWDMA

Would the above assembly into the proper SWDMA/MWDMA fix?

> compose such quickie in five minutes though.

I can wait some time for the proper fix but if you see that
it won't happen soon (week?) please send me this workaround.

Thanks,
Bart